Choosing odd man out of rotation

When Joe Saunders takes the Angel Stadium mound tonight, it will be more than a start. It will also be an audition, just like Jered Weaver’s start was Monday, and Ervin Santana’s will be Friday.

Come late September, Manager Mike Scioscia and pitching coach Mike Butcher will have a difficult decision to make: Which one of the five starters, who have had seasons ranging from very good to superb, will go to the bullpen for the playoffs?

John Lackey’s status as staff ace makes him a lock to start, and Jon Garland’s postseason success gives him a decided edge, so the final two spots probably will come down to the three younger pitchers, Santana, Saunders and Weaver.

“I couldn’t make that decision,” Saunders said. “That’s going to be tough. It could come down to whoever is hot in late September, or who is most comfortable coming out of the bullpen. . . . I’ll be down to do whatever is best for the team.”

Neither Saunders nor Weaver has pitched in relief in the big leagues. Santana made two relief appearances in 2007 and two in the 2005 playoffs, including a 5 1/3 -inning, three-run, five-hit effort in relief of injured Bartolo Colon in the Angels’ division series-clinching win over the Yankees.

Santana’s stuff -- he has a 96-mph fastball, nasty slider and changeup -- would fit nicely in a setup role, but the Angels also like the way it plays out over six or seven innings. Saunders is the only left-hander, and that could increase his chances of starting.

“You want to be one of the guys, but either way, it won’t bother me,” Weaver said. “Going to the playoffs is cool enough for me.”

Scioscia and Butcher haven’t broached the subject with their starters, “but they know it’s there, it’s no secret,” Butcher said. “It’s going to be tough, but we’ve done it as a team all year. We have to let it play out and see what happens.”

Pain in the neck

A bad baserunning decision by Erick Aybar on Monday night was compounded by an injury to the shortstop, who jarred his neck sliding head-first into third base and was too stiff to play Tuesday night.

Aybar, who was replaced at shortstop by Sean Rodriguez and in the No. 2 spot in the lineup by Howie Kendrick, could return tonight or Thursday.

“He has limited motion in his neck,” Scioscia said. “We want to get that out of there before he plays again.”

Injury updates

An MRI test on Garret Anderson’s left knee, which he injured making a play in left field Sunday, revealed tendinitis. But Scioscia said Anderson “feels good,” he was available to pinch-hit Tuesday and probably will return to the lineup tonight.

Vladimir Guerrero’s legs also felt better, and the right fielder took batting practice before Tuesday night’s game. Scioscia said Guerrero, who was given Monday off and did not start Tuesday, probably will start tonight.

Short hops

With his 14th homer of the season and 40th of his career Monday night, Mike Napoli passed Bob Boone to become the third player to hit at least 40 homers as a catcher for the Angels. Bengie Molina and Lance Parrish share the record, each having hit 61 homers as a catcher for the club. . . . When Francisco Rodriguez notched his 50th save Sunday, he became the youngest pitcher, at 26 years 7 months 17 days, to reach 50 saves. He also reached the milestone in 129 games, faster than any pitcher in history.

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mike.digiovanna@latimes.com