Milwaukee Brewers closer Devin Williams was diagnosed with two stress fractures in his back and is expected to miss around three months, sources told ESPN on Wednesday, a significant blow for the National League Central champions, who were relying on a deep bullpen to buttress a lack of high-end starting pitching.

“My understanding is it’s going to be six weeks of no throw just to shut him down, and then Devin will determine the pace beyond that,” Brewers general manager Matt Arnold said Thursday. “We just want to be extra cautious with him, and make sure he gets the good treatment that he needs.”

Brewers will open season without their All-Star closer. Devin Williams has stress fractures in back

Williams, 29, is a two-time NL Reliever of the Year and owns a career ERA of 1.89. With the trade of All-Star starter Corbin Burnes to the Baltimore Orioles and All-Star starter Brandon Woodruff out for the season following shoulder surgery, the Brewers’ bullpen was a weapon on which first-year manager Pat Murphy could rely.

“Any time you lose a pitcher of the caliber of Devin, it’s always a tough loss for sure. I don’t think there’s any way you can replace that necessarily,” Arnold said. “But we have a lot of guys that we believe in in our group, and somebody is going to take a step forward. … This early in camp, there’s still a ways to go to determine who that’s going to be.”

Arnold said the team would also be open to looking outside the organization for help.

Report: Brewers' Devin Williams Out 3 Months With Back Injury; Has 2 Stress Fractures | News, Scores, Highlights, Stats, and Rumors | Bleacher Report

Back specialist Dr. Robert Watkins diagnosed Williams with stress fractures on the left and right sides of his T12 vertebra, sources said.

He is expected to make a full recovery without surgery and return midseason.

Williams’ back issues started in September, but with Milwaukee in the midst of a pennant race, he pitched through them. Following Milwaukee’s wild-card series loss to Arizona, Williams took a month off before starting his offseason program. His back showed no issues coming into spring training, but it flared up during his first bullpen session and required treatment. During his second spring training outing, in which he allowed four runs in two-thirds of an inning, Williams noticed the back pain affecting his throwing mechanics and underwent an MRI.

Reports: Brewers' Devin Williams out three months with stress fractures in back

Watkins saw potential stress fractures, and further imaging Wednesday confirmed pars fractures — which come from repetitive stress — on both sides of Williams’ back, sources said.

Though the Brewers boast a deep array of relievers, including right-handers Abner Uribe, Joel Payamps, Trevor Megill, Bryse Wilson and Elvis Peguero as well as left-hander Hoby Milner, Williams is unquestionably one of the best in baseball.