This story was excerpted from Christina De Nicola’s Marlins Beat newsletter. To read the full newsletter, click here. And subscribe to get it regularly in your inbox.

ATLANTA -- Whenever Marlins left-hander A.J. Puk returns from the injured list, he will do so out of the bullpen.

Puk, who made the transition from reliever to starter over the offseason with 142 career Major League outings already on his resume, is currently sidelined with left shoulder fatigue. That -- rather than his production on the mound -- is the reason for the switch, according to manager Skip Schumaker.

“We're kind of still walking through that exactly on what that looks like -- if it's a few innings out of the bullpen, one inning -- we're not really sure,” Schumaker said. “We want to make sure he's healthy first, but I think you'll see him in the bullpen.”

Prior to being placed on the 15-day IL on Saturday, Puk compiled a 9.22 ERA, giving up 17 runs (14 earned) over 13 2/3 innings with 17 walks and 12 strikeouts. He was unable to complete at least five frames in each of his four starts.

To put those struggles into perspective, Puk was among baseball’s most dominant arms in four Grapefruit League starts. He allowed just three runs (two earned) in 13 2/3 innings for a 1.32 ERA while striking out 23 and walking four. Miami looked wise in proactively moving Puk into a starting role because right-handers Sandy Alcantara, Eury Pérez and Edward Cabrera as well as left-hander Braxton Garrett opened the season on the IL.

“He was really good in spring,” pitching coach Mel Stottlemyre Jr. said. “He struggled with some mechanics, struggled with getting the ball in the zone. I can't stand here and tell you whether it was self-inflicted and what thoughts were going through his mind, but something did change. He's going to come back and go back into the bullpen and probably be the same really good bullpen guy with probably less thinking and worrying about how to get [through] the lineup three times. He's still got four nice pitches. We may narrow some back down, and [it’s just about getting] him back in the zone attacking the way he was last year.”

Workload always was going to be something to monitor with Puk, who turned 29 on Thursday. He has never thrown more than 66 1/3 innings in a Major League season, and his career high as a professional is 125 frames in 2017 during his first full campaign. Puk also has dealt with injuries off and on, most recently missing time from May 13-June 5, 2023, with left elbow nerve irritation.

“Being healthy and keeping him healthy, we feel like this is the move for him right now,” Schumaker said.

Moving Puk back into a relief role also should help the bullpen, which has just two southpaws: closer Tanner Scott and setup man Andrew Nardi. If one happened to be unavailable for a game, that left Schumaker with limited options to mix and match in key situations. At one point last season, the Marlins had as many as five lefties in an eight-player bullpen: Scott, Nardi, Puk, Steven Okert and Matt Moore.

With Puk headed back to the bullpen, the club must decide on what to do when the fifth spot in the rotation comes around. Following Thursday’s off-day, Miami will begin a stretch of 13 consecutive days with games. Right-hander Sixto Sánchez overcame some first-inning issues in an otherwise impressive bullpen game on Wednesday, and Garrett is scheduled to resume his rehab assignment on Friday at Triple-A Jacksonville. He likely would need a couple of starts without setbacks to be reinstated.

“Another lefty, another good lefty, too,” Stottlemyre said of Puk in the bullpen. “And then we've got to answer the rotation piece. We'll get better in the bullpen, for sure.”