SAN DIEGO - When Cliff Lee completed his 10th inning of work on Wednesday, he pleaded for more. Lee had felt "a little something" near his ribcage during the 10th inning, but he still told pitching coach Rich Dubee he wanted the 11th inning against San Francisco.

"I didn't really think much about it, to be honest with you," Lee said.

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The next day, after the Phillies flew south to San Diego, the soreness lingered. The lefthander played catch Friday, and it was still there. On Saturday, he landed on the disabled list with a strained muscle in his left side.

Lee said the team debated whether it was necessary to guarantee at least 15 days on the shelf or simply skip one start. That would seem to indicate the injury is not serious, but ultimately Lee will not know until the prescribed rest takes effect.

He believes he'll miss only a few starts. He could be activated May 4.

"We erred on the side of caution and played it safe," Lee said. "I can't really argue with that, either."

Lee has had abdominal problems before. He has gone on the disabled list three times in his 11-year career with those injuries. But he claimed this muscle strain is different from the ones before it, which were lower in the abdomen.

The last Phillies starting pitcher to suffer a similar strain was Joe Blanton at the end of spring training in 2010. He spent 38 days on the disabled list and missed 24 games then. The Phillies do not believe Lee's injury is as serious, but typically, abdominal strains are problematic for pitchers. Phillies general manager Ruben Amaro Jr. conceded there is no way of knowing how much time Lee could miss.

Kyle Kendrick will start in Lee's place Monday in the series opener against Arizona.

Manager Charlie Manuel echoed Lee's comments.

"We've got Kendrick," Manuel said. "I feel comfortable with Kendrick. We've got the pitching to offset that. I got a feeling [Lee's] not going to be out long. When his time is up he's going to be back. I think we can definitely cover that."

Lee disputed the notion that pitching a 10th inning caused the injury. Nineteen times in 2011 he threw more than the 102 pitches he did in 10 innings.

"That didn't matter," Lee said. "I felt fine the whole time. I threw 102 pitches. I've thrown more pitches than that in five or six innings. I don't think that had anything to do with it."

Thome's bat

Jim Thome made only his third start of the season, and it was forgettable. He struck out twice and made an error at first that cost the Phillies a run.

The future Hall of Famer is 2 for 17 with nine strikeouts this season while adapting to a bench role for the first time in his career.

"He needs more than one start," Manuel said. "He definitely needs some at-bats. His timing is off. Thome's swing is there. What happens when you sit on the bench, the pitchers are ahead of you. The fastballs, they'll throw the ball by you."

Extra bases

Carlos Ruiz returned after a two-game absence with a sore left wrist. Ruiz was 1 for 4 and scored the team's lone run. He said after the game his wrist felt fine. . . . John Mayberry Jr. pinch-hit and struck out on a ball at his eyes. He has struck out in 13 of his 40 at-bats. . . . Pitching prospect Justin De Fratus, on the major-league disabled list with elbow soreness, pitched a scoreless inning at single-A Clearwater to begin his official rehab assignment.