BOSTON -- When it rains, it pours.

An hour before the Blue Jays’ losing streak slipped to five with an 11-5 loss to the Red Sox, No. 1 prospect Ricky Tiedemann walked off the mound in Double-A with a trainer, favoring his throwing arm.

Tiedemann, who is MLB Pipeline’s No. 28 prospect overall, released a breaking ball and immediately motioned for his catcher and the training staff. He’s been diagnosed with left biceps discomfort, but even if the full diagnosis proves to be minor, the fear of something worse highlights just how fragile Toronto’s pitching depth could be.

The Blue Jays’ rotation has already gone through three distinct stretches in 2023, from bad to good to bad again. Kevin Gausman allowed eight runs on 10 hits Thursday against the Red Sox, lasting just 3 1/3 innings, but the master of the splitter was coming off two dominant performances and should be just fine.

Adding salt to the wound, reliever Zach Pop left with a hamstring injury, which would cut further into Toronto’s pitching depth. In this age of pitching, rotation and bullpen depth can overlap.

“It’s tough to line things up properly,” manager John Schneider said. “A week ago, we were talking about how good our starters were and how deep they were going into games. It will ebb and flow like that and it will get back to normal.”

The worry here isn’t about performance, but about further injuries. Not even the luckiest clubs spend a season on the same, five-man rotation.

Tiedemann's MLB timeline

This all depends on Tiedemann’s full diagnosis, but the important factor here is that Tiedemann’s stuff is MLB-ready. It has been for a while now.

The final stages of his prospect development, like so many top young arms, is about establishing his day-to-day routines that prepare him for a full MLB season and building up his workload. It doesn’t happen overnight, but the Blue Jays have been extremely encouraged by Tiedemann’s commitment to the fine details. 

“He’s incredible in the way he goes about his work and the professionalism, just the way he goes about his business generally,” director of player development Joe Sclafani said near the end of camp. “Now, it’s about the consistency, getting to build his workload a little bit with longer starts and starting to refine how he attacks hitters with his stuff. The stuff obviously speaks for itself, but as he keeps climbing and gets closer, he’s going to have to figure out what works best for him. He can’t just out-stuff people any more.”

That final piece is so important, and will determine just how far Tiedemann goes. Any long-term injury takes 2023 out of the conversation, of course, but if this is a short-term injury, Tiedemann could still take a run at the MLB roster by August or September. What an ace up the sleeve he’d be for the Blue Jays’ bullpen if he has some bullets left.

Who else? The current depth options:

Right now, this conversation might start with Mitch White, who pitched to a 7.74 ERA after joining the Blue Jays last season and opened the season on the IL with an elbow issue. White is rehabbing with Triple-A Buffalo right now, and while he’s experienced as a bulk reliever, he’s being stretched out as more of a traditional starter for a reason.

Already on that Triple-A roster is Drew Hutchison, owning a 2.25 ERA after throwing exactly three innings in each of his four starts. Hutchison doesn’t have a spot on the 40-man roster, though, which Zach Thompson and No. 3 prospect Yosver Zulueta do. The only problem? Thompson has a 7.71 ERA and Zulueta's is 7.20.

A couple of months down the road, Hyun Jin Ryu will enter the picture. He’s been recovering from Tommy John surgery in the middle of June, 2022, but is progressing well through a comeback bid in the final year of his four-year, $80 million deal. Perhaps there’s a storybook ending, but again, that involves a lot of hope for a team with World Series aspirations.

Tiedemann wasn’t the next man up just yet, but he had a clear path to being just that in 2023, even at 20 years old who turns 21 on Aug. 18. Besides, we’re not talking about an urgent need tomorrow, this is about the reality that most MLB teams use 8-10 starters a season, at minimum. Until we know more about Tiedemann’s diagnosis, though, Toronto’s pitching depth is back in the spotlight for a worrying reason.