The Chicago Cubs got more information on reliever Julian Merryweather, who moved to the 15-day injured list on Sunday.

At the time, the Cubs indicated the injury was a right shoulder strain. But, after further examinations and tests, manager Craig Counsell said that Merryweather has a rib stress fracture in his back.

Counsell told reporters, including the Chicago Tribune, that Merryweather will be shut down for four weeks. At that point, Chicago may know more about his timeline for recovery, which will include a ramp-up period before being activated.

This is a big blow to the Cubs’ bullpen, as Merryweather had picked up where he left off from a season ago, his first in Chicago.

Last year he went 5-1 with a 3.38 ERA in 69 games. He threw 72 innings, striking out 98 and walking 36. He had two saves and 17 holds last season.

Before the injury, the right-hander had already made four appearances, striking out six and walking two in 4.1 innings with a 1.93 ERA.

This means, for the time being, Daniel Palencia will remain in the Cubs’ bullpen. The Cubs recalled him from Triple-A on Sunday after moving Merryweather to the injured list.

Palencia broke in with the Cubs last year, as he went 5-3 with a 4.45 ERA in 28.1 innings with two holds. He struck out 33 and walked 14 in 27 games. He stated last season at Triple-A.

The Cubs are in San Diego to start a three-game series with the Padres on Monday. After that, the Cubs will remain on the west coast to play series with the Seattle Mariners and the Arizona  Diamondbacks.