The Cubs’ rotation has had to go through adversity all year.

They might be facing their biggest test now.

The Cubs announced Wednesday that Marcus Stroman suffered a right rib cartilage fracture and there is no timetable for his return to the field.

“We’re going to kind of wait and see,” Cubs president of baseball operations Jed Hoyer said. “Obviously, it’s gonna be a real rest time. But unclear about what that means at that point. We’ll see.”

It’s a unique injury — Hoyer said it’s not an injury he’s seen before for a pitcher in his career — so it’s hard to gauge whether the righty will miss just a short amount of time or the rest of the season. The Cubs thought Stroman might start Wednesday against the White Sox, but due to the injury, Javier Assad took his spot in the rotation.  

“It was really one where we had no idea what it was,” Hoyer said. “Not your usual pitching injury. It’s not an arm, it’s not a shoulder, it’s not an elbow.

“After the bullpen on Sunday, we assumed he was gonna make the start [Wednesday]. So yeah, we were surprised.”

Stroman originally landed on the 15-day IL on August 2 with right hip inflammation. He received a cortisone shot and even then, said he would only be out for the minimum stay.

Stroman went ahead with his ramp up and the Cubs thought he had come out of the bullpen session OK. On the flight back from Toronto on Sunday, Stroman began to suffer discomfort and the Cubs weren’t sure what was causing it. He underwent an MRI on Monday that revealed the injury.

“I mean, I have no idea, that’s the honest truth,” Hoyer said. “We don’t really know at this point. I think we’ll obviously give him a real rest period and see how he feels. But I mean, again, it’s not a real common pitching injury. I’ve never seen that before. So, for me to speculate would be just false.

“At this point, we’ll just rest and hopefully he feels better and hopefully comes back and pitches really well.”

The Cubs rotation started the year with Kyle Hendricks on the IL as he recovered from a capsular tear in his shoulder. Then, the team dealt with struggles from top free agent addition Jameson Taillon. After a hot start that included a near-perfect game, Drew Smyly has undergone struggles and was moved to the bullpen.

Then, after a stellar first half that resulted in an All-Star Game appearance, Stroman went through his own struggles. In the finale of the London series in late-June, he suffered a blister and exited after just 3.1 innings. Since that game, he sports a 9.00 ERA and 1.93 ERA in 7 starts. Stroman had a 2.28 ERA and 1.02 WHIP in 16 starts.

“I mean, he hasn’t been pitching for us,” Hoyer said. “So I mean, we didn’t lose a pitcher that was active. We lost a guy that we thought was pitching today that was on the IL. So, we’ll move forward with the guys we have right now.