TUCSON, Ariz. -- Angels ace John Lackey is not expected to be ready to make his Opening Day assignment against the Athletics on April 6 at Angel Stadium.

"Right now, it's definitely unlikely," manager Mike Scioscia said on Friday.

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Lackey experienced tightness in his right forearm against the Royals during a 90-pitch effort on Sunday. After playing catch at the team's Tempe, Ariz., complex on Thursday, Lackey was "a little tight," Scioscia said.

An MRI was taken of Lackey's arm on Thursday. "The results, I think, were negative," Scioscia said.

Lewis Yocum, the team orthopedist, will be in camp on Saturday to examine the MRI results, a club spokesperson said.

"There's some inflammation we're dealing with," Scioscia said. "He's going to be on hold for a bit."

In Lackey's absence, with Ervin Santana already sidelined by a right elbow ailment, Joe Saunders is the logical candidate to assume the Opening Day assignment coming off an All-Star season. Jered Weaver would emerge as the No. 2 starter, followed by Dustin Moseley, Nick Adenhart and Shane Loux.

Kelvim Escobar, recovering from right shoulder surgery performed in July, could be back before May 1, Scioscia said. Escobar has been the story of the spring, reaching 96 mph on the radar gun in a Minor League camp game on Monday. The right-hander, an 18-game winner in 2007 who missed all of 2008, will pitch in another camp game on Saturday.

Lackey began to experience what he described as "some discomfort" in the fourth and fifth innings of his appearance against the Royals on a windy Sunday in Surprise, Ariz.

Asked after that game if he felt he was ready for Opening Day, Lackey gave what could be viewed in reflection as an intriguing response.

"I don't know if I'm ready physically," he said. "I'm ready mentally, I guess."

Lackey missed the first six weeks of the 2008 season with a strained triceps, finishing 12-5 with a 3.75 ERA in 24 starts. He also pitched Games 1 and 4 of the American League Division Series against the Red Sox, going 0-1 with a 2.63 ERA.

It was the first time in his career, going back to 2002, when he broke into the rotation at midseason, that he missed any time because of an injury. He is entering the final year of his contract, the Angels having picked up his $9 million option for 2009. 

Moseley, Adenhart and Loux came to camp thinking they would be competing for the starting job formerly occupied by Jon Garland -- until Escobar returned. But Santana's injury created another opening, and if Lackey starts the season on the 15-day disabled list, the defending AL West champions figure to open with three-fifths of the rotation having started a total of 30 Major League games.

Moseley, who has made 18 starts for the Angels over the past two seasons and 20 in his career, is 4-4 with a 5.91 ERA in those outings. The 27-year-old right-hander has been confident and productive this spring, going 3-0 with a 3.15 ERA in 20 innings pitched, striking out 15 hitters while walking five.

Adenhart, 22, has been considered the club's premier pitching prospect for several seasons. He struggled in three starts with the Angels last season -- he was 1-0 with a 9.00 ERA in 12 innings -- but has shown poise and maturity this spring. He's 2-0 with a 3.26 ERA in 19 1/3 innings, having struck out 13 against four walks.

Loux, 29, made four impressive outings this spring before getting knocked around by the Diamondbacks on Friday. Loux was out of baseball in 2007 but made an impressive return after signing a Minor League contract with the Angels. He was the Pacific Coast League's Pitcher of the Year in 2008, going 12-6 with a 3.98 ERA.

Loux hasn't started a Major League game since he was with the Tigers in 2003, when he was 1-1 with a 7.12 ERA. He has made seven career starts in the Majors.

Last year, Santana and Saunders came to camp fighting for the fifth spot in the rotation. Both ended up making the AL All-Star team after Lackey and Escobar began the season on the DL.

Making his fifth Cactus League start on Sunday in Surprise, Lackey departed having faced six batters without getting an out in the fifth inning. Alberto Callaspo and Mike Jacobs went deep, joining the home run party.

Lackey made it through 3 2/3 innings having allowed only one run, on Ryan Shealy's homer, while the Angels were racking up nine runs in the first two innings against lefty Horacio Ramirez. The first of two Miguel Olivo homers came in the fourth against Lackey.

Almost doubling his pitch count to 90, Lackey -- who'd thrown in the bullpen after an economical 50 pitches in his previous outing -- lost some command in the fifth.

"I got a little tired, and the ball was going up a little," Lackey said, adding that he needed to "push through it, keep getting stronger."

Scioscia saw some fatigue in Lackey's final inning, adding, "He was supposed to get to about 90 pitches today."