BOSTON -- Red Sox slugger Triston Casas provided details Friday on his left rib cage injury that will keep him sidelined for a minimum of a few weeks.

The first baseman revealed he has torn cartilage. There was no break in the bones of his rib cage.

“No ribs were fractured,” Casas said. “It's not a bone thing. It's more a cartilage thing. So there's the ribcage and then there's the sternum, and there’s pieces of cartilage that are in between those that connect the two. And that was what was torn, was the cartilage.

“The way that the doctors kind of explained it to me is that one isn't better than the other. [Whether the injury] was a muscle or a bone or cartilage, they’re all similarly timetabled schedules. Everything in the midsection just takes a long time to heal and mend, and there's a lot of torque and rotation that happens during the swing, so everything needs to be perfect.”

In other words, the cartilage needs to heal fully before Casas can ramp back up for a return to action.

Was the 24-year-old given any kind of timetable from the doctors for how long the healing process might take?

“They said anywhere from three weeks to six weeks to nine weeks, “ Casas said. “They don’t know. It’s just depending on how my body is feeling. But for right now, I'm still in pain to breathe. My lungs are still hitting my midsection which I’m still getting to like 75 percent capacity without pain.”

Even without a precise timetable, Casas expressed confidence that he will be back in the lineup for a significant portion of the 2024 season.

“Very optimistic,” Casas said. “I'm feeling better right now with movement every single day. I haven't really thought about the progress I've made in these last couple days. So I'm happy about where I'm at compared to where I was feeling five days ago. So hopefully, I keep getting better every day. That's the plan, and I can hit the ground running right when I get off the IL. So yeah, I anticipate playing for a good amount of the season.”

Casas knows there are no shortcuts he can take in the process of returning to the active roster.

“The first step is to feel good breathing before I can move to cardio and then move into more anaerobic exercises and then progress as I go there,” Casas said. “But that's the first step to feeling better is just breathing without pain. So that's what I'm working on now.”

Casas came out of Boston’s game at Pittsburgh on April 20 after fouling off a 3-1 pitch left him wincing in pain. The injury had started to form in his first at-bat against Ben Lively in a game against the Guardians three days earlier, but the left-handed hitter didn’t realize at the time how significant it would be.

“After that, I was trying to manage it with the trainers, but it was a couple of days, and my body gave in [on April 20],” Casas said.

The doctors indicated to Casas that the injury wasn’t from a specific movement, but likely from years of swinging the bat ferociously with his 6-foot-5 frame.

“From what the doctor explained to me, he said that he had seen these types of injuries in football players and hockey players,” Casas said. “And he had asked me if I had had a collision in the past of some sort that would merit some pain in my midsection. And I told him, ‘No.’

“And he pretty much chalked it up to me being so big, rotating so fast so many times that I pretty much created a car crash within my body. And it was a matter of time before this happened. He said it was something similar to a pitcher needing Tommy John, just an inevitable thing that was going to happen sooner or later.”

As for Casas, a key cog in Boston’s lineup, he just hopes his return is sooner rather than later.