The Phillies placed Keller on the 15-day injured list Thursday with a torn UCL in his right elbow.
Keller returned from the injured list July 8 after missing nearly a month due to forearm tendinitis, but he'll now likely miss the remainder of the season because of his latest injury. If he decides to undergo surgery to address the issue, he would likely miss most, if not all, of the 2027 campaign, as well. Seth Johnson will come up from Triple-A Lehigh Valley to fill the vacancy in Philadelphia's bullpen.