The Orioles are preparing for the absence of catcher Matt Wieters, who could leave on the paternity list as early as Saturday to be with his wife, Maria, for the birth of their second child.

Manager Buck Showalter said he spoke with his All-Star catcher about the medical plans, which seem fluid, though he seems to be accounting for the period of time between Saturday and Tuesday.

“You know, he doesn't have to take all three” days allotted on the paternity list, Showalter said. “He could take one, he could take two, a maximum of three. So obviously, his priority and our priority is for him to be there for his wife and family. I know a lot of the details that I'm not going to bring up. That's their private affairs.

“But I think it's probably going to be something, somewhere between the range of Saturday through Tuesday where we're going to have to do something — somewhere in that area.”

Showalter said Wieters' wife has an early-morning appointment with a doctor Saturday. If Wieters needs to begin his absence that day, Showalter said, the Orioles would be able to add a roster replacement in time. That extra player would almost certainly be a catcher, with Triple-A catcher Francisco Pena the only option already on the 40-man roster. Pena hit .219 with a home run in nine games while Wieters' primary backup, Caleb Joseph, was on the disabled list with a testicular injury suffered on a foul tip.

Wieters is batting .240 with 10 home runs this season, his August batting average buoyed to .256 by a five-hit game Sunday in San Francisco.

Tillman to start Saturday night: One of the bigger health scares of the Orioles season seems to have come to a quiet resolution, with right-hander Chris Tillman on track to start Saturday after being bumped from Wednesday night's rotation spot with shoulder discomfort.

Tillman threw a flat-ground session in the outfield at Camden Yards on Thursday under the supervision of bullpen coach Dom Chiti — standing in for pitching coach Dave Wallace, who is home tending to a personal matter — and assistant athletic trainer Brian Ebel.

“He's ready to go for Saturday,” Showalter said. “I'm glad we took the time.”

Tillman initially felt the discomfort last Friday, the morning after he pitched a gem against the Oakland Athletics to stop the Orioles from being swept in a four-game series there. By Wednesday, he said he'd probably have been able to start if the team needed him to.

But the caution appears to have paid off, with the team's top starter taking his 15-4 record and 3.46 ERA to the mound Saturday.

O'Day's absence could linger: Reliever Darren O'Day might not be back as early as the Orioles initially expected, with Showalter saying he might not return from the DL when he's eligible Aug. 27 or even when rosters expand Sept. 1.

O'Day is “inching forward, little by little,” Showalter said, as the setup man waits for marked improvement after getting a cortisone shot to alleviate rotator cuff soreness in his right shoulder.

Around the horn: Thursday marked the first start in a week for designated hitter Pedro Alvarez, who sat with no DH allowed in San Francisco and with the Orioles facing the Boston Red Sox's two left-handed starters. … Showalter said right-hander Dylan Bundy, who rolled his ankle Wednesday while trying to field a ground ball, didn't have any lingering effects.

jmeoli@baltsun.com

twitter.com/JonMeoli