Reliever Julian Merryweather will be shut down from throwing for at least four weeks, after imaging showed a rib stress fracture in his upper back, Cubs manager Craig Counsell revealed on Monday.

The Cubs put Merryweather on the 15-day injured list Sunday with what they initially called a right shoulder strain. But he was scheduled to undergo further tests at the time.

“Candidly, we thought it would be a little shorter stay on the IL, but that’s the breaks,” president of baseball operations Jed Hoyer said Monday. “Obviously we have to let him heal. … Probably a little worse diagnosis than we had imagined, and we’ll just have to get through it.”

Counsell said Merryweather’s injury hadn’t been a lingering issue. In his last outing, Merryweather held the Dodgers to one hit through 1 ⅓ innings Friday, entering with traffic on the bases and allowing just one inherited runner to score.

The last hitter he faced was Shohei Ohtani, who Merryweather induced to fly out. But the right-hander “felt something,” on one of his last pitches, Counsell said.

“Didn’t think much of it, frankly, after the outing,” Counsell said. “And then the next day it was sore, and the next day it was sore as well.

Losing Merryweather disrupts the flow of the back end of the bullpen. In close games, Counsell has typically used Merryweather and Mark Leiter Jr. in late innings before turning to setup man Héctor Neris and closer Adbert Alzolay.

In a right-handed heavy bullpen, Leiter matches up well against left-handed heavy pockets of lineups. Merryweather’s fairly even splits and ability to throw multiple innings gave Counsell flexibility in how he chose to use him.

“Julian is a valuable reliever on this team, for sure,” Counsell said when asked about filling Merryweather’s role. “So, I don’t see it being one person. You’ve got to close the hole around him, and a lot of people are going to have to fill into that spot. But it’s a significant loss, for sure. His versatility, just the quality that he brought, is going to be missed.”

Hoyer addresses pitching injuries

A rash of high-profile MLB pitchers sustaining elbow injuries has brought the debate over pitcher health to the forefront in recent days. Over the weekend, the Guardians’ Shane Bieber and Braves’ Spencer Strider were among those who their names to a growing list of UCL injuries.

“It’s a real industry-wide concern, and we’re part of the industry,” Hoyer said. “We have three pitchers on the IL right now that we were planning on playing a significant role. Three out of 13 guys, that’s a lot. I think for everybody, it’s a real concern.”