In a significant blow to the first-place New York Yankees, closer Luke Weaver is expected to miss four to six weeks because of a hamstring injury, sources told ESPN’s Jeff Passan on Monday.

Weaver suffered the injury over the weekend during the Yankees’ three-game series against the Los Angeles Dodgers. The right-hander logged an inning in Saturday’s 18-2 blowout loss, giving up a home run and throwing 14 pitches. He warmed up to pitch the ninth inning in Sunday’s series-ending win but felt discomfort in his hamstring while stretching after completing the warmup and did not enter the game.

Afterward, Yankees manager Aaron Boone said Weaver would undergo tests Monday in New York during the team’s off day. The Yankees are scheduled to begin a three-game series against the Cleveland Guardians at Yankee Stadium on Tuesday.

Weaver continued his dominance from his breakout 2024 campaign, posting a 1.05 ERA and holding opponents to a .412 OPS across 24 outings this season. He began the year as the primary setup man for Devin Williams before replacing Williams in the closer role in late April. He has converted eight saves in nine opportunities.

The Yankees are expected to place Weaver on the injured list Tuesday with Fernando Cruz slated to be activated. Williams figures to slide back in the closer role. The two-time All-Star hasn’t given up a run in 11 of his past 13 appearances, lowering his ERA from 11.25 to 6.23 over the span.