Just four innings back after a 19-month absence, Miles Mikolas faces another period of time on the mend.

The Cardinals right-hander was removed from Saturday’s game -- a 2-1 victory over the Cubs at Busch Stadium -- with right forearm tightness and was placed on the 10-day injured list on Sunday. Mikolas had tossed some warmup pitches before the fifth frame, motioned to the trainer in the dugout, then was promptly removed from the contest -- his first game since the 2019 NLCS.

Initial MRIs showed no structural damage to Mikolas’ right elbow/forearm area, manager Mike Shildt said prior to Sunday’s series finale against Chicago. Mikolas will receive additional testing before determining a firm course of action.

It’s a positive development to glean no damage from imaging, but “the reality is that there's been a setback,” Shildt said on Saturday.

Concerning for Mikolas is the nature of the ailment. He had surgery to repair the flexor tendon in his right forearm last July, which kept him out of the shortened 2020 season, and then was derailed by shoulder inflammation and a minor impingement at the outset of this past Spring Training.

Mikolas’ surgery last July was to try to get ahead of a more serious injury. His ailment in spring was due to throwing too full-bore after being absent from a Major League mound for a prolonged period of time. This injury is the third to his throwing arm in less than two years.

“There's obviously frustration, none more so than I'm sure with Miles; there's been a lot of time, energy and effort in rehab, like a real pro,” Shildt said. “ … You can't ever resemble and replicate what the environment was here last night in a rehab setting. … It's a cause for concern for a number of reasons, and Miles is frustrated with it, and we'll just have to get back to the drawing board and figure out what it looks like so he can come back and not have that be an issue.”

Before the fifth inning, there was nothing of obvious concern. Mikolas navigated early traffic and was solid in his last three frames, needing just 39 pitches for his final nine outs after 20 for the opening frame. He threw five pitches for three punchouts -- all with velocity down from his 2019 averages, though he’s expressed his need to pitch with more feel than overpowering speed as he worked back from his latest shoulder ailment.

Put another way: “He looked like old Miles,” Shildt said.

Mikolas self-reported the discomfort as he warmed up before the fifth inning. He called catcher Yadier Molina out to the mound, gestured toward the dugout and was lifted after a prompt discussion with head trainer Adam Olsen, Shildt and pitching coach Mike Maddux.

“He said, ‘On my slider, I'm feeling something that doesn't feel quite right, and I can push through it,’” Shildt recalled. “And of course I said, ‘No, we're not going to push through anything.’”

Daniel Ponce de Leon replaced Mikolas, after pitching one inning Friday night, and recorded five crucial outs without conceding a hit to save a taxed bullpen for the comeback victory.

The loss of Mikolas represents a derailment for the Cardinals' rotation the very same day it returned to full health for the first time this season. Amid a stretch of 17 consecutive games without an off-day, Mikolas’ activation provided an operable six-man rotation for the gauntlet -- and those plans will be re-evaluated after the upcoming series against the White Sox, with No. 9 prospect Johan Oviedo the most likely candidate for a callup.

Carlson update

Dylan Carlson (back tightness) was held out of the starting lineup for the second consecutive day after being a late scratch on Saturday. The right fielder was receiving treatment before Sunday’s finale, and he was available only in an emergency situation, Shildt said after the 2-1 loss to the Cubs. The Cardinals hope another 24 hours will allow Carlson’s back to heal more fully; he’ll be re-evaluated in Chicago.

Lane Thomas earned his second consecutive start in right field in Carlson’s absence, after hitting the game-tying base knock for Saturday’s ultimate victory.

Pitching plans

The Cardinals set their rotation for the upcoming three-game trip against the White Sox, which will pit Shildt against his longtime mentor and Cardinals Hall of Famer Tony La Russa for the first time.

Kwang Hyun Kim will face former Cardinal Lance Lynn in Game 1 on Monday, with longtime friends and high school teammates Jack Flaherty and Lucas Giolito sparring in Game 2 on Tuesday. John Gant will oppose Carlos Ródon, who threw a no-hitter in April, for the finale on Wednesday.