MESA, Ariz. -- Cubs pitcher Ted Lilly, rehabbing from arthroscopic surgery on his left shoulder, was experiencing some soreness in his right knee and may undergo an MRI Thursday as a precautionary measure.

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"Hopefully, it's just a minor little thing," Cubs manager Lou Piniella said of Lilly's knee. "As far as his shoulder is concerned, he's gaining strength and feeling good. We're just having to hold him back so he doesn't take a step backwards."

Lilly was to be examined late Thursday. He said his knee was "barking a little bit."

"I ran on it yesterday, and it's not something I'm going to make a big deal out of," he said. "I'm just going to have it looked at."

Last July, Lilly needed arthroscopic surgery on his left knee, and he joked Thursday that maybe he's a little "fragile."

His shoulder, though, feels strong.

"My shoulder feels good, and I'm real optimistic about that," Lilly said. "I'm happy with the way it's coming along. I have expectations to not be too far behind."

Thursday was a light workout day for the pitcher, and he threw for about 10 minutes from 90 feet. If his knee allows him, Lilly will stretch his arm out more on Friday and increase the intensity.

"We're holding him back as much as possible," Piniella said. "We've got plenty of time with Teddy to get him ready. We don't want him to get overanxious."