NEW YORK -- Kodai Senga's return from a right shoulder capsule strain that has kept him from pitching for the New York Mets this season has hit another snag.

The right-hander underwent an MRI on his triceps Friday that revealed nerve inflammation, Mets manager Carlos Mendoza said.

Senga, according to Mendoza, will receive a cortisone shot and will be shut down for "three to five days" before being reevaluated. Whenever he resumes throwing, Senga will need to build up playing catch before pitching off a mound again.

The development is potentially a major setback for Senga, who will need a monthlong minor league rehab assignment before joining the Mets once healthy. He had a planned bullpen session canceled Sunday because he was experiencing tightness in the triceps. Mendoza at the time reported a "low level" of concern for the 2023 National League Rookie of the Year runner-up.

"We were able to take a look at, not only the shoulder today but the elbow, the whole thing just to make sure we're not missing anything," Mendoza said. "Good news: It's just inflammation. Like I said, getting this shot and hopefully he can get going from here now. So, it's one of those things that we knew from the beginning he was going to take time and here we are dealing with it."

Senga, 31, reported arm fatigue in February upon reporting to spring training as the team's ace after posting a 2.98 ERA with 202 strikeouts last season.

He was finally trending toward a rehab assignment last week after slowing his progression recently to focus on improving his mechanics. He told reporters earlier this month that he felt his mechanics weren't right during his first live batting practice session April 29 and again in his next session May 4. He said he believed the issue could lead to poor performance and further injury.

An injury surfaced anyway. How significant remains to be seen.

For now, the Mets must continue trying to stay afloat in the standings without their top starter.