BOSTON -- Starter Aaron Cook is throwing again as he recovers from a left knee laceration that required 11 stitches.

Cook injured his knee when he was spiked in a collision at the plate in his Red Sox debut May 5.

"He still has the stitches in there, but he's kept his arm in good shape," manager Bobby Valentine said. "We're trying to simulate some throwing, so he throws and sits down and throws and sits down, so when it is time for him to pitch again, he doesn't have to start from the two-inning stint. He might be able to throw five innings and have his arm built up to that 70-75 pitch barrier."

The right-hander is eligible to return from the 15-day disabled list May 21, when the Red Sox open a three-game series at Baltimore. The club was unsure if Cook would pitch a simulated game or make a rehab start in the Minors before returning.

"I have no idea. I mean, I have an idea, but it's still hypothetical," Valentine said.

Cook allowed six earned runs on eight hits in 2 2/3 innings in his only start with the Red Sox. He didn't have a defined role on the pitching staff and was filling in for Josh Beckett, who missed one start with lat stiffness.

Youkilis swings bat, could return on road trip

BOSTON -- Third baseman Kevin Youkilis is in the home stretch of his rehab from a lower back injury, but he was not quite ready to return to the roster on Monday, the first day he was eligible.

That gave top prospect Will Middlebrooks at least one more day in Boston's starting lineup. Fresh off his fourth home run in 10 games, Middlebrooks batted fifth in manager Bobby Valentine's lineup.

The way Youkilis is ramping back up, he could return any day. Perhaps Wednesday, when the Red Sox open a three-city road trip, would be the logical time for Youkilis to be activated.

"I have no idea," Valentine said. "Whenever the medical [staff] and Kevin say he's ready. All I'm saying is my eyes saw him take some ground balls and he looked good throwing, fielding. I wouldn't think he's very far away. He took 10 swings on a soft toss and about 30 dry swings. He's going to hit some balls today. He looked really good moving around."

But here is the question all Red Sox fans want to know: What becomes of Middlebrooks once Youkilis returns?

"I think that's a little premature," Valentine said. "We'll do exactly what's right. Those things, they usually play themselves out. No need to really make a decision until it's time to make a decision."

General manager Ben Cherington told csnne.com last week that Youkilis would retain his job once he was healthy.

Valentine was asked before Monday's game if there could be a scenario in which Middlebrooks would be a bench player rather than go back to the Minors.

"Sitting on the bench is not the place for very many players, especially good young talented players," Valentine said. "What would be the purpose of having someone sit the bench unless there was a useful purpose not being in the starting role but also being able to contribute to the team's wins? Now is there a place for him to do that? I'm not sure."

As for Middlebrooks, his start has been somewhat historic. According to Elias, Middlebrooks is the third player in Major League history to accumulate at least four homers and 13 RBIs in his first 10 games. The others? Alvin Davis with the 1984 Mariners and Mark Quinn for the 1999 Royals.

Nava making strong second impression

BOSTON -- When Daniel Nava resurfaced last week from Triple-A, it was unclear how often he would surface in manager Bobby Valentine's lineup. As it turns out, Monday marked the fifth time Nava started in the five games he's been back.

As the old saying goes, sometimes the player actually writes out the lineup instead of the manager.

Nava certainly put himself in position to get a sixth straight start based on what he did Monday during the Red Sox's 6-1 win over the Mariners.

Not only did Nava reach base three more times, but he even produced his second career home run, and first since the grand slam he hit on the very first pitch in his career on June 14, 2010.

Nava went nearly two years -- and 171 Major League at-bats -- between homers.

"Yeah, it was kind of a long time," Nava deadpanned after the game.

In his first five Major League games since 2010, Nava is 7-for-12 with six runs scored, four doubles, one homer, six RIBs and six walks.

"It's been phenomenal," said Valentine. "Every hitter, when they're in that zone, says they're seeing the ball well. This was my first time really looking at him closely from the right side. He's fouling off the tough pitches. He's taking the balls very early very confidently. He's putting a good swing on strikes. That's a hitter's wonderland. He's in it, and I hope he can stay in it for a long time."

Nava is relishing his latest chance to stick in the Majors.

"Honestly, I didn't know what to expect," Nava said. "I wasn't sure the role. I don't know, maybe it's just going day to day right now. That's the role. That's fine, it keeps things simple. You don't have to worry about anything. I was focused on one thing at a time, but I didn't know what to expect. I think that most guys coming up are pretty much not sure what to expect."

While his offense has been impressive, Nava's defense in left field has been noticeably better than during his rookie season.

"I had to make some adjustments. I had to learn to be more attentive on the defensive side," Nava said. "I probably wasn't as focused and didn't take it as seriously as I should -- at least in the Minors to when I came up here [the first time].

"I admit to that. Since that point, I've tried to be more attentive of swings and pitches and where I should be playing and checking my center fielder and aware of where he's going, because I had to learn that a little inch or foot can make a difference between a guy getting a hit or not getting a hit or scoring. I tried to put myself in the best possible situation to be in the right spot."

What else has changed for Nava from 2010?

"I think just getting to do it that second time around helps me understand how to go about my business and what to expect," Nava said. "Any time you do something a second time around, there's a comfort factor. That's helpful."

After getting an invite to Major League Spring Training in 2011, Nava was relegated to Minors camp this year. Some might have viewed that as a slap in the face that took him totally off the radar screen. Nava thinks it might have played an indirect role in him earning a ticket back to Boston.

"I didn't feel like it was a, 'Hey, we forgot about you.' I felt like what it just allowed me to do was focus on what I can control," Nava said. "Just be ready. I looked at it like, 'If I make the team, great. If I don't, at least I'll know that I gave it everything I had.' I think it took a lot of pressure off. I felt like I had nothing else to lose. Sometimes that's a good spot to be in."

Ellsbury building strength in injured shoulder

BOSTON -- Center fielder Jacoby Ellsbury is at least one month away from returning to the Red Sox, but the club is pleased with his progression from a right shoulder injury.

Ellsbury nearly has full range of motion after suffering a partially dislocated shoulder April 13, when he was trying to break up an inning-ending double play against the Rays.

"He just looked good in the weight room, he looks good in the training room," said manager Bobby Valentine. "Now I haven't seen him in the field of dreams out there where it's all green and he looks so natural. He hasn't had any setbacks. So it's all good."

The Red Sox placed Ellsbury on the 60-day disabled list Sunday to clear room on the 40-man roster for Mauro Gomez, who was recalled from Triple-A Pawtucket to replace injured outfielder Darnell McDonald (right oblique strain). The earliest possible return for Ellsbury is now June 13, though that could be a stretch.

"We can start counting days for the best-case [scenario], but it's going to be after that," Valentine said.

Ellsbury, 28, is building his strength and working on his agility and cardio.

"He's worked really hard on those things with his legs," Valentine said. "He looks really good."

The Red Sox don't anticipate Ellsbury needing shoulder surgery. Monday's game against Seattle was the 28th contest Ellsbury missed since going on the disabled list April 14.

Marlon Byrd made his 18th start in center field Monday. Ryan Sweeney made his first three starts of the year in center field during Boston's previous four-game series with Cleveland.

Consul General of Japan gives Sox cherry tree

BOSTON -- The Consul General of Japan in Boston, Takeshi Hikihara, presented the Red Sox with a cherry blossom tree before Monday's series opener against the Mariners. The gift was in honor of Fenway Park's 100th anniversary.

The cherry tree will be planted inside Gate B at Fenway Park and move to Yawkey Way when it is fully grown.

"Japan and the United States share many common cultural values, including a great love of baseball, and Fenway Park is indeed a treasure to both Japanese and Americans living here," Hikihara said.

Red Sox president/CEO Larry Lucchino, manager Bobby Valentine and starter Daisuke Matsuzaka accepted the tree in a ceremony before the game.