A weeklong break to rest Adbert Alzolay and his balky arm was ideally what the Chicago Cubs closer needed to be set for the final three weeks of the regular season.

Instead, Alzolay landed on the 15-day injured list Monday with a right forearm strain. The move was retroactive to Sunday, setting up his earliest return as Sept. 25 ahead of the Cubs’ final six games.

“I don’t think he felt like he can really help us right now, and that’s concerning,” manager David Ross said. “When you feel that way as a competitor, you want to go out there and compete. It’s hard to compete with the role he’s in at 75%. So making sure he’s healthy and being able to compete at the highest level is a real priority for him and us and protecting him.”

Alzolay’s forearm had bothered him for a few weeks. He was able to manage it and continue to pitch, but throwing in back-to-back games Friday and Saturday after seven days between appearances didn’t pay off like Alzolay and the Cubs had hoped. He won’t throw for a few days before testing his arm.

The injury affected Alzolay’s ability to get his breaking balls down in the zone. Once it also started affecting how he threw his sinker Saturday, he became concerned.

Alzolay hopes his IL stint follows the same path as Justin Steele’s and Michael Fulmer’s when they were briefly sidelined by the same issue this season. The Cubs activated Fulmer as the corresponding move for Alzolay.

“I wasn’t making a lot of competitive pitches out there because I just couldn’t reach my release point,” Alzolay said. “It doesn’t feel comfortable to go in a 1-0 game knowing you’re not 100%.”

Alzolay’s injury presents another challenge for the Cubs’ heavily used back end of the bullpen. Not being able to add a veteran reliever at the trade deadline was concerning, and now the Cubs must navigate their upcoming stretch without Alzolay’s consistency.

His 1.02 WHIP ranks sixth among National League pitchers with at least 50 outings, and he has walked only 12 batters in 63 innings, two of which came Saturday. Alzolay, who has a 2.71 ERA, has walked 1.71 batters per nine innings, the lowest figure in the NL and fifth-lowest in the majors (minimum 50 games).

The Cubs were quickly tested Monday in their series-opening 5-4 win against the Colorado Rockies. With right-hander Julian Merryweather unavailable after pitching three straight days, Ross called on José Cuas, Drew Smyly and Fulmer in high-leverage spots over the final three innings with mixed results.

“The one thing I appreciate tonight is the back end of the bullpen when they’re healthy,” Ross said.

The Cubs are unlikely to designate one player to take over Alzolay’s closer role. As Ross and pitching coach Tommy Hottovy have done throughout the year, they will look to set up relievers for the right pocket of the opposing lineup.

Six pitchers have recorded at least one save for the Cubs this year: Alzolay (22), Mark Leiter Jr. (four), Brad Boxberger (two), Fulmer (two), Merryweather (one) and Keegan Thompson (one), who is back at Triple-A Iowa.

“We’ll match them up as best as possible,” Ross said of his high-leverage options, “and do the best with what we’ve got.”

Smyly views Alzolay’s absence as a chance for everyone else in the bullpen to step up. Smyly did his part in Monday’s victory, tossing 1 2/3 scoreless innings. Since being moved back to the bullpen after his Aug. 22 start, Smyly has allowed two runs in 7 2/3 innings (2.35 ERA) with two walks and 12 strikeouts in five appearances.

“You want to pitch in meaningful games, you want to pitch in close games, you want to help the team and not just pitch to fill an inning or two,” Smyly said. “So every opportunity I get out of the pen, I’m going to try to prove that I can help and be valuable in that role ... keep continuing to build and try to gain some trust.”