New York Yankees closer Luke Weaver, who sustained a hamstring injury over the weekend, is expected to be sidelined four to six weeks, ESPN reported on Monday night.

After throwing 14 pitches in one inning during an 18-2 loss to the host Los Angeles Dodgers on Saturday, Weaver stopped warming up to pitch the ninth inning of New York's 7-3 win on Sunday due to hamstring discomfort.

New York manager Aaron Boone told reporters after the game that Weaver would undergo testing, and ESPN reported that the right-hander underwent an MRI. Per the report, the length of Weaver's absence will be determined on Tuesday.

The Yankees, who lead the American League East by 5 1/2 games, open a three-game series against the visiting Cleveland Guardians on Tuesday.

Weaver, 31, has excelled out of the Yankees' bullpen this season, going 1-1 with a 1.05 ERA and 0.701 WHIP in 24 games spanning 25 2/3 innings. He took over for struggling closer Devin Williams in late April and has eight saves in nine chances this season.

Williams, a two-time All-Star, likely will return to the closer role. The 30-year-old right-hander has lowered his ERA from 11.25 to 6.23 with 13 scoreless outings in his last 15 appearances. For the season, the 2020 National League Rookie of the Year is 2-2 with five saves spanning 21 2/3 innings in 25 games.

Right-handed reliever Fernando Cruz, 35, is slated to take Weaver's roster spot when the latter is expected to land on the injured list on Tuesday. In 21 relief appearances this season, Cruz is 1-2 with a 2.66 ERA in 23 2/3 innings.

Cruz last pitched for New York on May 17 before landing on the IL due to inflammation in his pitching shoulder.