Struggling with his command in two starts this season, Haren has allowed 20 hits in just 10 1/3 innings. The right-hander has also failed to reach the sixth inning in back-to-back starts for the first time since July 2009.
On Thursday against the Twins, Haren (0-1) lasted just five innings, giving up three runs on nine hits. However, he did strikeout seven and walk only one for the no-decision.
"With Danny, his first couple of starts, the ball has definitely been up a little bit," Angels manager Mike Scioscia said. "This guy's a total command guy, and he's uncharacteristically getting into some hitting counts."
Meanwhile, Tyson Ross will make his season debut for the A's as their No. 5 starter after starting six games last season for the club.
In two outings with Triple-A Sacramento this year, the right-hander tossed nine innings, giving up four runs with three walks and four strikeouts.
In four career games against the Angels, including two starts, he has a 2.45 ERA.
"He definitely is a talented guy," A's manager Bob Melvin said. "When he gets on a roll, you've seen here what we can accomplish."
A's: Cespedes gets night off
Yoenis Cespedes, having played the A's first 10 games, got the day off Monday, allowing Coco Crisp to play in his natural center-field position for the club's four-game series opener in Anaheim.
"All the other outfielders have had one," Melvin said.
The A's will celebrate the 40th anniversary of their 1972 World Series title on Friday and Saturday when the Indians are in town. The two-night celebration will feature appearances by Hall of Famer Rollie Fingers, Cy Young winner and American League MVP Vida Blue, World Series MVP Gene Tenace and All-Stars Bert Campaneris, Joe Rudi and Ken Holtzman, among others.
Angels: Cassevah close to return
Manager Mike Scioscia said Monday that righty reliever Bobby Cassevah is close to returning after he began the season on the disabled list with shoulder inflammation.
Cassevah hasn't allowed a run in each of his four one-inning outings with Class A Inland Empire, with his velocity improving since he began throwing there.
Even with a late flight Sunday night that resulted in his team not returning home until early Monday morning, Scioscia opted to play most of his regulars in Monday night's 6-0 win over Oakland.
The only change Scioscia made defensively was putting Peter Bourjos in the outfield for Bobby Abreu. Kendrys Morales also got the start at designated hitter over Mark Trumbo.
On Monday night in the first inning, Morales crushed an 0-2 fastball from A's pitcher Brandon McCarthy over the center-field wall at Angel Stadium for his first home run since May 29, 2010. That's the day Morales hit a walk-off grand slam against Seattle only to break his left ankle jumping into the home-plate celebration scrum after rounding the bases.
A's lefty Tommy Milone, scheduled to pitch Thursday against C.J. Wilson in Anaheim, was not feeling well Monday afternoon after experiencing food poisoning and was sent back to the team hotel before game time to rest.