Marcus Stroman is just as perplexed as the Cubs as to how he suffered a right rib cartilage fracture.

The righty threw a bullpen session on Sunday in Toronto and felt relatively fine throughout it. But when he started going through his cool-down process, the veteran righty started to feel some discomfort.

“Just was kinda like hard to breathe, kind of like in my diaphragm, rib area,” Stroman said on Friday.

The team wanted to rule out anything that would have caused trouble on the flight back to Chicago, including ruling out appendicitis or anything with his gallbladder. Once that was clear, he flew back to Chicago and immediately went to the emergency room.

“I went to the ER, was there for 3 hours — ruled out appendicitis, gallbladder,” Stroman said. “Woke up, I got an MRI and now I’m here. I don’t have any answers as far how I got it.”

And there’s no timetable on when or if he’ll be back this season.

“I’m taking it day by day, truly not even looking past tomorrow, man,” Stroman said. So, I don’t have an answer for you on that.”

The plan now for Stroman is to rest — he won’t begin any sort of baseball activities until he’s pain-free.

“I talked to several doctors that I’ve talked to over the past years with my body and I guess the best thing is kinda heal itself and it’s hopefully a few weeks,” Stroman said. “I can’t go anywhere. I can barely turn right now. Breathing’s tough at some points, to sit for long periods of time is pretty difficult. So I’m just taking it day by day honestly.”

His injury is the latest setback for a Cubs’ rotation that has dealt with some hiccups all season.

“Oh man, I’m the biggest believer of this team, you guys have heard how I’ve talked about this team since spring training. Nothing has changed,” he said. “I think we’re right in the thick of it. You see how we’re playing. I truly believe we could win the division and once you’re in the playoffs, it’s anyone’s game. No one’s a bigger believer in the Cubs than me.”

And he still hopes he can be a part of that.

“We’re in a playoff push and hopefully I can contribute,” Stroman said. “I’m just taking it day by day. I don’t wanna take away from anything we have going on right here, because we’ve been playing incredibly well and like I said everyone’s in a great space. I wanna make sure everyone stays in a great space and continues to do their thing.”