Aaron Boone didn’t sound overly optimistic late Sunday while discussing Luke Weaver, who had to cut his warm-up short in the bullpen before the ninth inning of that night’s game at Dodger Stadium because he “felt something” in his left hamstring.

Boone’s fears were soon confirmed.

The Yankees announced on Tuesday that the closer, who underwent an MRI on Monday, had been diagnosed with a left hamstring strain and was placed on the 15-day injured list. Though the Yankees declined to give a timeline for Weaver’s return — “Hopefully it’s on the shorter end of things,” Boone said — injuries of that nature typically have a recovery time of 4-6 weeks.

“I was very blindsided by the fact [that] this happened,” Weaver said in the clubhouse Tuesday before the Yankees started a three-game series against the Guardians at the Stadium.

Weaver, as he was last season, has been the most consistent arm out of what, overall, has been a standout Yankees bullpen, posting a 1.05 ERA in 24 games. The righthander was 6-for-7 in save chances since taking over for the struggling Devin Williams in late April.

Before Tuesday’s game, Boone said Williams would assume closer duties in Weaver’s absence.

“We’re talking about a guy that’s been a high-end closer,” Boone said of Williams.

Williams, who had a 10.00 ERA at the time of his demotion, has mostly pitched well since then. Going into Tuesday, Williams had not allowed a run in 13 of his 15 outings since his demotion, striking out 20 and walking five in 13 2⁄3 innings.

“I’ve seen a guy who has done what he’s done his entire career,” Weaver said of Williams. “He’s at full force right now . . . I know we got a stud pitcher, I know we’ve got one of the elites in the game and, when he is at his peak, there’s not much that can be done on the hitter’s side. He’ll be completely fine.”

Still, piecing the bullpen together without Weaver will be a challenge. Weaver was the club’s most valuable bullpen piece last season — his first full year with the Yankees — excelling in whatever role Boone chose to deploy him in and posting a 2.89 ERA in 62 appearances.

That especially proved to be the case in early September, and throughout the postseason, when Weaver assumed closer duties from an erratic Clay Holmes, who had 13 blown saves when the Yankees decided to make the switch.

After the Yankees acquired Williams, a two-time All-Star with the Brewers, Weaver, without complaint, started this season in the role he served in much of last year, and had been even better.

“Huge,” Boone said of the impact of missing Weaver. “I mean, he’s been one of the best relievers in the sport now going back to last year and, obviously, early this year. Definitely a blow, but one that I think we can handle and withstand.”

One of Boone’s key pieces from the first two months — and a pitcher who could help mitigate the loss of Weaver — returned Tuesday as Fernando Cruz was reinstated from the IL. The righthander, who struck out 35 in 23 2⁄3 innings, landed on the IL May 22 with right shoulder inflammation. Cruz will be one option for Boone on days Williams isn’t available to close, as will righthander Mark Leiter Jr. and maybe — depending on matchups — lefthander Tim Hill.

“I know we have six, seven guys capable of doing the job,” Weaver said. “We have an elite bullpen, we’ve been pitching unbelievable. Obviously, we ran into a little bit of a buzz saw there in LA. The games just kind of get a little messy sometimes . . . They can do it without me. There’s no lack of confidence.”

Boone said leftfielder Jasson Dominguez, who was not in Tuesday’s lineup, was “day-to-day” with the left thumb contusion the outfielder suffered sliding into second base in the fifth inning of Sunday night’s win over the Dodgers “I was a little concerned, honestly, yesterday and the day before,” Boone said, noting the swelling that had been detected in the thumb area. “But it seems like it’s gotten better every day, and everything looks like it’s just going to be a couple day thing. Hopefully that’s the case.”