MIAMI — The Marlins placed rookie right-hander William Kempner on the 15-day injured list with a right elbow sprain, the fifth reliever sidelined this season for a bullpen that is running out of healthy arms.

The 25-year-old Kempner, who opened his big league career with 10 scoreless innings, struggled in both outings this week before the move. He recorded just one out while allowing two runs on two hits and two walks Thursday against the Mariners, then surrendered another two runs over two frames in a 42-pitch outing Saturday against Cleveland. Miami recalled rookie left-hander Dax Fulton as the corresponding roster move prior to Sunday’s 5-2 loss to the Guardians at loanDepot park.

Kempner told MLB.com the discomfort had been weighing on him mentally before he flagged it to the club. “I think [you say something] at the point where it’s affecting your mind going into the game, and for me, going in, up until I’m actually standing on the game mound, it’s nagging at me, and I’m in the bullpen trying to throw pitches, and I’m rubbing out my elbow to make it loosen,” Kempner said. “And I just thought, ‘If I’m focusing on this, I can’t be actually focusing on my job that I have to do in the game.’”

Kempner underwent further imaging, though the Marlins did not announce details of the results. Manager Clayton McCullough said the pitcher had been dealing with forearm discomfort for several weeks while working on his sweeper. “You go through a season,” McCullough said, “and [Kempner] felt something periodically in his forearm for several weeks, and he’d been working on his sweeper. That might have just led to some of the tension there, and he mentioned it to us yesterday, and was going to go get some imaging done today. Certainly a pitcher’s arm, different story, especially the forearm area. We felt it was certainly going to be enough to warrant an IL stint.”

Kempner joins a growing list of sidelined relievers that includes veterans Anthony Bender (right shin stress reaction), John King (left lateral ankle sprain) and Andrew Nardi (rib cage stress reaction), along with rookie Josh Ekness (right calf strain). Fulton’s recall gives Miami a fresh arm but does little to address the depth problem that has left McCullough with fewer and fewer options in late-inning situations.

Kempner is eligible to return after the 15-day IL stint, though the club has not provided a timeline for his recovery.