Yankees pitcher Jonathan Loaisiga makes the play for an out...

Yankees pitcher Jonathan Loaisiga makes the play for an out on a ball hit by Arizona Diamondbacks' Joc Pederson in the ninth inning during a baseball game, Wednesday, April 3, 2024, in Phoenix. Credit: AP/Rick Scuteri

The Yankees officially have lost one of their most potent bullpen arms for the season. Jonathan Loaisiga revealed Saturday that he’ll undergo surgery to repair a UCL issue that landed him on the 60-day injured list a day earlier.

The exact nature of the surgery is unclear: Loaisiga said it will remedy damage to his UCL, with Aaron Boone adding that the Yankees are unsure if he’ll require Tommy John surgery. The club had called it a right flexor strain on Friday. The initial estimate for his return is 10 to 12 months, Loaisiga said. If he does indeed end up needing a second Tommy John surgery, that timeline balloons to 16 months, he said.

This is the latest in a slew of debilitating injuries for the Yankees' hard-throwing setup man, who pitched in only 17 games last season while battling two bouts of elbow inflammation. He also had surgery last May to remove bone spurs in that elbow.

The Yankees took a conservative approach with Loaisiga during spring training, but that apparently did little to protect him from injury. Righthander Dennis Santana, who impressed in spring training, was signed to a major-league contract and added to the active roster Friday to help buoy the bullpen.

“Very frustrating — really tough,” Loaisiga said through an interpreter. “Last year, the injury took me out of the game for quite some time. This year, after this, I’m going to end up losing the rest of the season. Tough moment to deal with, but at the same time, there’s a will inside and I want to be out there pitching. You have to use that as motivation and rely on that to carry you through a moment like this.”

He added that the injury is “very different from last year — completely different . . . One of the pitches I made in that game [against the Diamondbacks on Wednesday], I felt the pressure right away. Right now, the extension is very limited in the elbow right now.”

Loaisiga, who didn't allow a run in four innings in three relief appearances this year, said he injured himself throwing a changeup to the last batter he faced Wednesday. He underwent an MRI Thursday, which revealed what the team termed a “right flexor strain," and consulted with doctors Friday.

“It’s a significant forearm strain,” Boone said. “Obviously, it’s tough news . . . You feel for him. He’s throwing the ball so well. He’s just dealt with things the last few years that have added up to this point.”

Loaisiga didn’t know when the surgery will be performed but said it will be done by Dr. Keith Meister. Loaisiga previously had Tommy John surgery as a minor-leaguer in 2016 and also has battled shoulder injuries.

“It’s kind of been pretty much something every year that’s either tripped him up, sometimes for short periods of time and sometimes longer,” Boone said. “Hopefully, whatever road he goes down here, this is something that serves him well moving forward in his career because he’s a really good pitcher.”

Loaisiga is set to hit free agency at the end of this season, meaning this could be his last time in pinstripes.

“My mind is not there right now — my mind is what I need to do next,” he said. “You’ve got to have a lot of patience when you go through something like this and you’ve got to keep your faith strong and you have to work through it and keep a positive mind and find strength to get yourself back here.”

DJ on the mend. DJ LeMahieu  took batting practice Friday for the first time since fouling a ball off his right foot  on March 16 and suffering a non-displaced fracture, and he reported Saturday that he was encouraged by his progress. LeMahieu said he intends to ramp up baseball activities with more batting practice, baserunning and fielding ground balls this week. “I’m hoping to have a really good week of baseball activity,” he said.

After that, the Yankees will evaluate his progress and potentially have some sort of timeline for his return. He still has to graduate to lateral movement.

“He let it rip and didn’t feel inhibited at all, which is good,” Boone said of LeMahieu’s batting practice. “We’ve just gotta keep moving that needle.”

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