Lynn was pulled from his final start of spring training with right knee discomfort -- one of a series of injuries for the reigning AL Central champions already this season.
Third baseman Yoan Moncada is out with a strained right oblique and ace right-hander Lucas Giolito is on the 10-day injured list due to a lower abdominal strain. Relievers Joe Kelly (right biceps nerve injury), Garrett Crochet (left elbow surgery) and Ryan Burr (strained right shoulder strain) also are on the IL, along with outfielder Yermin Mercedes (fractured left wrist).
Left fielder Eloy Jimenez and second baseman Josh Harrison left Wednesday night's 6-4 win over Seattle. Jimenez was sidelined by a left ankle contusion, and Harrison was dealing with lower back stiffness.
X-rays were negative on Jimenez's ankle, but manager Tony La Russa said Jimenez and Harrison likely will be out of the starting lineup for Thursday's series finale against the Mariners.
Lynn went 11-6 with a 2.69 ERA in 28 starts last season in his first year in Chicago. He had surgery this month and is expected to be sidelined for four to six weeks.
"I'm ahead of schedule. But we'll see how that goes because there's still a lot of work left to do," Lynn said. "We've got some time till I get on the mound. Everything's good right now. We just need to make sure we stay on that pace."
Lynn, who turns 35 on May 12, said the big test will be when he gets back on the mound.
"When it comes to mound time, that's going to tell us everything we need to know," he said. "Anything you do, stress-wise, on flat ground is not near as much as it is on the mound. So we'll see, when it comes to that time, how we feel. And then after that, it's building that pitch count, and that takes a minute."
Still, Lynn wasn't the only one feeling good about his rehab process.
"I've seen him walking without a limp. He's feeling good," manager Tony La Russa said. "Gio just said he threw and didn't really feel it. Some positive progress. Survive and thrive, man."