FORT MYERS, Fla. — The late Earl Weaver, legendary manager of the Baltimore Orioles, used to talk about the “deep depth” a team needed to make it through a marathon baseball season.

The Boston Red Sox were reminded of that on Saturday afternoon at Jet Blue Park.

Eduardo Rodriguez – slated as the No. 4 starter in the Sox rotation and considered by some to be a budding ace – went down in a heap while running through routine pop-up drills on one of the back fields in the complex. The 22-year old Rodriguez instantly thought the worst.

“Am I going to pitch again?” Rodriguez wondered aloud to reporters. “Am I going to have to wait a long time?”

Fortunately for Rodriguez, that does not seem to be the case. He was diagnosed with a subluxation of the patella (an knee injury to most of us) and was expected to be throwing after 72 hours on the shelf. Even if it takes a little longer, Rodriguez should have plenty of time to get ready for April.

There are very few spots up for grabs on the 2016 Red Sox. You could predict the 25-man opening-day roster with better than 90 percent accuracy. The only real spot open right now is for a left-handed reliever, and Tommy Layne has the inside track for that (with Robbie Ross Jr. expected to be the other lefty in the bullpen).

That can all change in the blink of an eye. Or the fielding of a pop-up. Which is why it’s important to see how Henry Owens does in his spring training starts (he makes his first one Wednesday against Minnesota). Keep a close eye on Brian Johnson’s recovery from an elbow injury last year. Pay close attention to how Steven Wright’s knuckleball is dancing in Grapefruit League games.

Rarely do you make it through the baseball season on the strength of five arms. Last year 12 pitchers started games for the Red Sox. Only two of them made more than 25 starts. Five pitchers made their first major league starts. It was all hands on deck, the way it often is with last-place teams.

That’s why Dave Dombrowski, Boston’s president of baseball operations, added an ace to the rotation this winter. The Red Sox spent $217 million to acquire the services of David Price.

The mere presence of Price is supposed to make the rest of the starting rotation better, yet there are still plenty of question marks surrounding the durability of this starting staff. Clay Buchholz is notoriously fragile and has been on the disabled list in each of the last six seasons (and seven of the last eight). Joe Kelly has missed significant time to injuries in each of his last two seasons. Rick Porcello missed nearly a month with a right triceps strain last year.

Then came Rodriguez’s fall on Saturday.

It’s a far cry from the 2004 Red Sox, who got 157 starts out of their five-man rotation. Such staffs are rare indeed.

If Boston’s starters break camp healthy, Owens and Johnson will start the season in Triple-A Pawtucket. The Sox think highly of both pitchers, which is why they didn’t trade either in the offseason. Roenis Elias was acquired from Seattle (along with Carson Smith) in the Wade Miley trade, and could beat out Layne as the team’s second lefty reliever. Elias split time between the Mariners’ rotation and bullpen and could fill a hole should one arise in Boston. Wright, now out of options, is likely to stick as a long reliever and a pitcher ready to make a spot start.

But things happen. The Sox believe they’ve built a roster to compete for the AL East title in 2016. Chances are, they’ll need help from pitchers you’re not thinking about right now.

In other words, they’ll need to see if their depth is deep enough.

Tom Caron is a studio host for the Red Sox broadcast on NESN. His column appears in the Portland Press Herald on Tuesdays.