SAN DIEGO — When Cliff Lee completed his 10th inning of work last 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.

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 only miss 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 than 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. admitted 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 vs. Arizona. Kendrick made 15 starts in 2011 and has acted as the long man in the bullpen this season. He threw a 20-pitch bullpen session Saturday to stay sharp, but he'll probably on a limited pitch count.

Charlie Manuel echoed Lee's comments that it could be a brief absence.

"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 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."

Contact Matt Gelb at mgelb@phillynews.com or follow on Twitter @magelb.