LOS ANGELES — With Tim Lincecum complaining of an upset stomach, the Giants sent their young ace back to San Francisco on Thursday to be examined by a doctor.

Manager Bruce Bochy received a preliminary report that Lincecum's exam did not turn up any health issues, and the right-hander is expected to start Saturday against the Arizona Diamondbacks.

"I believe he is going to be fine," said Bochy, "but this is why we sent him back — to rule out any concerns. "... He has been a little sickly the last couple months. It's zapped him a little bit."

Lincecum was sick twice in spring training, including a nasty bout with bronchitis, and has appeared gaunter than his listed weight of 170 pounds. It's a likely explanation for the drop in velocity while he has posted a 7.56 ERA in two starts

"His effortless fastball had been 95 mph, and now it's 91," Giants pitching coach Dave Righetti said. "He's trying to generate power. You'll overthrow and go too fast if you sense you're short. If you come out of your delivery just enough, the ball starts running over the plate.

"He went through that at times last year. People keep forgetting he pitched an entire game against Atlanta out of the stretch."

In addition to his two illnesses this spring, Lincecum wasn't able to throw on the side for a few weeks because he split the nail on his middle finger in his second Cactus League start.

"At least we're able to work on stuff now," Righetti said.

Lincecum threw a vigorous side session Wednesday and Righetti said he was encouraged with it. Prior to the session, Lincecum said he had noticed a few irregularities on video.

"My mechanics are linear," said Lincecum, who led the NL in pitches thrown last season. "I'm trying to make two things do one thing. I have to stay on a straight line toward the plate, like I'm doing a cartwheel. At the same time, I'm turning in a circle the other way when I turn my back. I've been turning too much and I'm not getting where I need to be."

Righetti said he isn't worried about Lincecum's velocity as much as his ability to make pitches. But he knows others are panicking. "I totally understand it because he's the reigning king — the Cy Young guy," Righetti said. "Everyone goes through things like that and he's gotta learn from it."