Triston Casas first felt the discomfort after a swing against Ben Lively during last Wednesday’s shutout of the Cleveland Guardians at Fenway Park. The Red Sox first baseman thought it was an abdominal issue, but after trying to tough it out for a few days it eventually became clear this wasn’t an injury he could play through.

Now Casas is likely to miss several months with what the club described as a rib fracture, though after a series of examinations he likened to an anatomy lesson, Casas explained his injury is actually a bit more complex than a simple bone break.

“No ribs were fractured, it’s not a bone thing, it’s more of a cartilage thing,” Casas said in the Red Sox clubhouse Friday afternoon. “So there’s the rib cage and there’s the sternum, and there are pieces of cartilage that connect the two, and that’s what was torn.”

Casas said he was told by the doctors that his injury is much more common in football and hockey players, and he was asked if he’d been involved in any collisions that would merit some pain in his midsection. When he told them no, the doctors chalked it up to his being so big and rotating so fast so many times when he swings that his body couldn’t hold up.

“I pretty much created a car crash within my body, and it was a matter of time before this happened,” Casas said. “He said it was something similar to like a pitcher needing Tommy John, just an inevitable thing that was going to happen sooner or later.”

The good news is this injury isn’t any better or worse than if he’d fractured a bone or pulled a muscle, as all would have a similar timetable of several months. The bad news is there isn’t anything he can do but wait for the cartilage to heal, and there isn’t much clarity over how long that could take.

“They said anywhere from three weeks to six weeks to nine weeks, they don’t know, it’s just depending on how my body is feeling,” Casas said. “Right now I’m still in pain to breathe, my lungs are still hitting my midsection. I’m still getting to like 75% capacity without pain, so the first step is to feel good breathing before I can move to cardio and then I’ll move into more anaerobic exercises and progress as I go there.”

Even still, Casas said he’s optimistic he’ll be back in time to play a meaningful portion of the season, and that once the injury heals it shouldn’t take long to get back into game shape.

“It’s not something he said I’m going to need to manage, he says once it mends correctly I’ll be able to hit the ground running and keep going,” Casas said. “There won’t even need to be a rehabilitation process, just a strengthening process of the abdominal area to continue my swing progression.”

As for whether there’s concern he could suffer an injury like this again — much like some pitchers need Tommy John surgery more than once — Casas said his understanding is that once the cartilage heals, his whole abdominal area should be more durable, making a recurrence less likely down the road.

“Hopefully with all the blood and enzymes and nutrients that’s going to my rib cage hopefully it heals and mends stronger,” Casas said. “Typically whenever you get injured it comes back a little stronger, so my hope from all of this is I come back swinging the bat faster and a little more durable and I’m hoping my body can grow into my midsection so I can continue playing the game healthy like I know I can.”