The Cubs will be without their ace for a while.

Justin Steele was placed on the 15-day injured list Saturday with a left hamstring strain, retroactive to March 29. To replace him on the pitching staff, the Cubs are calling up top pitching prospect Ben Brown.

The Steele news was expected after manager Craig Counsell indicated as much following Thursday’s heart-wrenching season-opening loss in Texas. It’s a tough blow to a team that entered 2024 with expectations firmly set on a playoff run.

The Cubs are expecting Steele to be out until at least May.

“The MRI showed a Grade 1 hamstring strain, which frankly, as we showed him walking off the field, is probably better than at least I anticipated,” Counsell said Saturday before his team’s 11-2 loss to the Rangers. “And just how he was walking after the game. Really, he’s much better today. He played catch today, which is a great sign.

“He’s gonna miss the month of April. Beyond that, it’s really about, in a couple days, when his gait gets back to normal, laying out a plan. It’s how much can we do with his arm going up to when we’re healthy? And then it gets more complicated with starters and these guys’ return to play. How many times are we going to have him go out and pitch before he pitches for us?”

Steele, 28, is the unquestioned ace of the staff and one of the top starting pitchers in all of baseball. He finished 5th in National League Cy Young voting last year and made the All-Star team for the first time.

Before departing with the injury on Thursday, he had 6 strikeouts and allowed a lone run in 4.2 innings.

Brown, 24, is a tall right-hander (listed at 6-foot-6) whom the Cubs acquired from the Phillies at the 2022 trade deadline in a deal for veteran reliever David Robertson.

Brown stands as the Cubs’ No. 10 prospect on Lance Brozdowski’s updated 2024 rankings and he sits at 3rd among pitchers on the list behind Cade Horton (2nd) and Jordan Wicks (8th).

The Cubs added Brown to the 40-man roster after the 2022 season but he has not yet made his MLB debut. The former 33rd-round pick in the 2017 Draft spent most of last year in Triple-A, posting a 6-8 record with a 5.33 ERA and 1.53 WHIP with a whopping 100 strikeouts in 72.2 innings.

The Cubs plan to use Brown out of the bullpen initially, though he can provide length and may end up joining the rotation.

“He’s available out of the bullpen today and then we’ll move forward from that,” Counsell said Saturday. “I expect him to definitely be involved in some length or a start — whatever you want to call it — at some point. But today, out of the bullpen.”

Brown did end up pitching out of the bullpen Saturday, tossing 44 pitches in 1.2 innings in his MLB debut. He was tagged for 6 runs on 5 hits and 2 walks in that time and struck out 1 batter.