ST. PETERSBURG -- The Yankees announced that they claimed outfielder Darnell McDonald off waivers from the Red Sox on Wednesday.

McDonald, who was designated for assignment by Boston on Saturday, will join the Yankees' active roster on Friday, when they start a four-game weekend series at Fenway Park against the Red Sox. With Boston starting three left-handers in four days and a day-night doubleheader scheduled for Saturday, Yankees manager Joe Girardi expects the right-handed-hitting McDonald to play this weekend.

"We're going to see three lefties," Girardi said. "He's going to play the outfield some this weekend."

The Yankees will have to make a corresponding move on the 25-man roster when McDonald is activated, but Girardi mentioned the possibility of putting Andruw Jones at designated hitter or giving center fielder Curtis Granderson one of Saturday's games off.

A fan favorite in Boston, McDonald batted .214 with a .678 on-base plus slugging percentage this season, hitting two homers and collecting nine RBIs while playing all three outfield positions.

McDonald first announced the move on Wednesday afternoon on his Twitter account, @MacDime54, saying he "just got off the phone" with Yankees general manager Brian Cashman and was "happy to announce I'm a new Member of the N.Y.Y."

To make room for McDonald on the 40-man roster, the Yankees designated right-hander Chris Schwinden for assignment.

Girardi patient despite Martin's struggles

ST. PETERSBURG -- Despite Russell Martin's season-long struggles at the plate and his rough night behind it during Tuesday's 7-4 loss to the Rays, Yankees manager Joe Girardi reiterated on Wednesday that Martin is still the club's starting catcher.

Martin owned up to his poor hitting after Tuesday's game, saying he has become overaggressive and stopped swinging at his pitch.

"If I really knew, then I probably wouldn't be struggling as much," said Martin, who entered Wednesday's series finale at Tropicana Field batting .182. "Really probably just expanding the zone a little bit too much, not being patient. I don't know when's the last time I walked, but it's normally a big part of my game."

Martin has drawn 28 walks on the year but only six since May 30, and none since June 20. That has Martin's on-base percentage at .302, more than 50 points below his career average of .355.

Girardi didn't think Martin was letting that affect him defensively, even after he committed two errors and let the Rays steal five bases on Tuesday night.

"If every time a guy had a bad night defensively you thought it was because of his offense -- they're going to have bad nights defensively, too," Girardi said. "I don't think he's carrying it over, no."

"I haven't been really good all year offensively," added Martin. "I've always been able to kind of separate those. It's even more frustrating when you're not doing either, and [Tuesday] was one of those days."

Bombers bits

• Right-handed reliever Joba Chamberlain, rehabbing from a torn medial collateral ligament in his right elbow and a dislocated right ankle, will pitch his first simulated game on Friday in Tampa, Fla. Chamberlain promised on Monday that he will pitch for the Yankees this season.

• Girardi said that outfielder Brett Gardner, on the disabled list with a right elbow strain, should begin taking dry swings within the next day or two.

• Girardi saw catching prospect Austin Romine (lower back strain) catch a bullpen session on Wednesday morning and estimated that Romine is a few weeks away from returning.

• The Yankees haven't received the results from tests run on rehabbing reliever David Aardsma. The right-hander, working his way back from Tommy John surgery, was shut down late last week. Girardi believed the club was waiting on an opinion from Dr. Lewis Yocum, who performed Aardsma's surgery.

• Girardi said the Yankees haven't made a decision yet on what they'll do with right-hander David Phelps after his start on Wednesday. CC Sabathia is expected to return to the rotation after the All-Star break, and Phelps isn't scheduled to make a start in the Boston series.

• The USO Liberty Bells were on hand to sing the national anthem at Tropicana Field prior to the first pitch between the Yankees and Rays on the Fourth of July. That was followed by the ceremonial first pitch from Col. Lenny Richoux. Tampa Bay's mascot, Raymond, was also dressed in Uncle Sam attire.