PHOENIX -- In the third inning of his start against the Angels on Monday, Diamondbacks right-hander Ryne Nelson felt some discomfort in his elbow after throwing a pitch.
But when he threw his next pitch at 98 mph and didn't feel any pain he thought nothing of it and decided not to say anything to the training staff as he finished up his seven-inning outing without any further issues.
When he was taken out of the game, Nelson told team trainers, and after giving it a day or so of treatment he tried to play catch. It didn't go well, and Thursday he underwent an MRI that showed a flexor muscle strain and a mild ulnar collateral sprain.
While the news is not the worst case scenario -- that would have been a torn UCL that required Tommy John surgery -- it's not good news for the Diamondbacks, as Nelson will be shut down for four-to-six weeks before having another MRI taken. If that MRI is clean, he would need to build his pitch count back up.
That would seem to peg sometime in September for his return.
"Just disappointed," Nelson said. "It's not the news that you want to hear. It's also not worst case, so there's a little bit of a bright side to it, but just gonna do whatever I can to get back healthy and get back out there and help this team win."
It's yet another piece of bad news for the Diamondbacks on the pitching front. Recently, it was determined that ace Corbin Burnes suffered a setback in his recovery from Tommy John surgery, and the best-case scenario for his return appears to be September as opposed to the hoped-for mid-July return.
Closer A.J. Puk, who was also working his way back from Tommy John surgery and was out on a rehab assignment, was diagnosed with a shoulder capsule sprain, and he will be shut down from throwing for four weeks before being re-evaluated.
"That's also another big loss," Diamondbacks manager Torey Lovullo said of Puk. "A.J. was doing all that he could to get back here and join us."
In 15 starts this season, Nelson has produced a 4.97 ERA with a 1.24 WHIP. He is in his fifth Major League season with the Diamondbacks after being selected in the second round of the 2019 Draft out of Oregon.
The injury to Nelson and the delayed return of Burnes will test the Diamondbacks depth of starting pitching.
For now, right-hander Yilber Díaz was recalled from Triple-A Reno to provide an arm in the bullpen, but the Diamondbacks will need to find someone to make Nelson's scheduled Sunday start.
One option is to go with Merrill Kelly, who would be pitching on regular rest since the Diamondbacks had Thursday off. They also could call up a starter from Reno.
One option that seems off the table at the moment is Brandon Pfaadt, who was removed from the rotation in late April and moved to the bullpen. Pfaadt was optioned to Reno earlier this month with the idea of building his pitch count back up so he could eventually start again.
As of now, though, it doesn't seem like he's there yet, as he threw 45 pitches in his most recent start last Sunday.
"I don't think his workload is where we want it right now to come back up and compete," general manager Mike Hazen said. "So we'll figure it out."