Reid-Foley exited his outing Saturday night against the Philadelphia Phillies while facing J.T. Realmuto in the eighth inning. The right-hander fired high on a 2-0 count and immediately motioned for a trainer.
New York said an MRI on Sunday morning showed a partially torn ulnar collateral ligament and Reid-Foley would meet with team doctors and medical staff to discuss treatment options. Tommy John surgery could be a possibility.
"It's unfortunate. But we're lucky in today's world it's something that can be fixed," manager Buck Showalter said.
Working as a middle reliever and long man with the ability to pitch multiple innings, Reid-Foley has a 5.40 ERA with no record in seven appearances this season. He has struck out eight and walked seven in 10 innings.
Right-hander Yoan Lopez was recalled from Triple-A Syracuse to fill the bullpen spot.
Reid-Foley was one of three young pitchers acquired by the Mets from Toronto in a January 2021 trade that sent lefty Steven Matz to the Blue Jays. The 26-year-old right-hander, born in Guam, was chosen by the Blue Jays in the second round of the 2014 amateur draft out of high school in Florida and is 7-9 with a 4.66 ERA in 40 major league games, including 13 starts.