SAN FRANCISCO -- Playing catch in the outfield at Oracle Park on Saturday morning, the D-backs' Merrill Kelly felt a light sensation in his shoulder on four or five throws, just enough to alert the right-hander that something might be amiss.

Kelly was examined by team trainers and sent for an MRI. He got a preliminary reading of the MRI, but he will fly back later Sunday to Phoenix, where he’ll have the imaging looked at on Monday by team doctors. From there, they will formally diagnose Kelly's ailment and determine if further tests are needed.

“All we know now is it’s kind of a mild teres major stain,” Kelly said before the D-backs' 5-3 win over the Giants at Oracle Park. “I don't know necessarily the grade of [the strain]. I don't know, kind of the timeline or anything like that.”

Kelly had been scheduled to start Sunday’s series finale against the Giants, but he was scratched and right-hander Slade Cecconi was recalled from Triple-A Reno and took his place, recording the first quality start of his career as he tossed six innings of one-run ball. Kelly has yet to be placed on the injured list, though that seems almost certain to happen. Instead, reliever Justin Martinez was optioned to Reno.

Kelly missing any time is a significant blow for the D-backs as he has been one of the most consistent pitchers in baseball over the last four seasons, combining with Zac Gallen for a formidable 1-2 punch at the top of the Arizona rotation.

The loss of Kelly is just the latest in a rash of injuries that have hit the D-backs over the last month.

It started towards the end of Spring Training when lefty starter Eduardo Rodriguez went down with a lat strain. He was followed by closer Paul Sewald going on the IL with an oblique strain.

The injuries didn’t stop once the regular season got going as shortstop Geraldo Perdomo (right meniscus tear) and outfielder Alek Thomas (strained left hamstring) each ended up on the IL. Right-hander Ryne Nelson lasted two innings in his start against the Giants on Thursday night before being struck on the right elbow by a line drive and that forced him to the IL as well.

“I can't explain why it's happened, or at the rate in which it's happening,” D-backs manager Torey Lovullo said of the injuries. “It's a little uncommon. But we've got to keep pressing forward.”

Kelly developed blood clots in his leg last year, which required a stint on the IL. The right-hander had thoracic outlet surgery in 2020, but this injury is a different experience for him.

Kelly prides himself on being a workhorse and reaching the 200-inning mark in 2022 was important for him. Last year, it wasn’t the regular-season innings that added up as much as his season lasting into November as the D-backs made a run to the World Series. Between the regular season and postseason, Kelly threw 201 2/3 innings, the most he's tossed in a single year in his career.

Given that workload, the D-backs took things slowly with Kelly this spring. He did not make his first Cactus League appearance until March 8.

Kelly, 35, was asked what he thought could have contributed to the injury.

“I think that's probably an impossible question to answer,” he said. “With what we do for a living -- obviously throwing is a completely unnatural motion. Not to say that I'm old, but you know, I do have some miles on my arm. I've been fortunate enough to get to this point without having any [arm muscle] problems, but most guys in this locker, most guys in this league, they're going to experience something in their careers and this just seems to be you know, my time to deal with that.”

Cecconi took Kelly’s place Sunday, but what the D-backs do going forward remains to be seen. Brandon Pfaadt will take his regular turn Monday against the Cardinals and Jordan Montgomery will stay in line and pitch Wednesday in St. Louis.

The D-backs have not announced a starter for Tuesday, which would have been Nelson’s turn in the rotation. They could go with Logan Allen, who pitched well in relief after Nelson got hurt and is stretched out as a starter. Or they could look to recall lefty Tommy Henry, who was optioned to Reno last week when Montgomery joined the rotation.