MIAMI -- An MRI revealed mild inflammation in the back of the right shoulder of Marlins top prospect Sixto Sánchez, the club announced on Friday afternoon. The 22-year-old right-hander, who reported slight discomfort during a simulated game on Wednesday night, was prescribed a few days rest and will then begin rehab with slow progression on a throwing program.

"I thought the news was pretty good," Marlins manager Don Mattingly said during a Zoom call. "Obviously, you don't want anything to be major. Just having to take care of him and allow this process to work its way through. I'm feeling like you're going to get Sixto back at some point or getting him here at some point is a good thing."

After a late arrival to spring camp because of visa issues out of the Dominican Republic, Sánchez also had a false COVID-19 positive test that set him back a couple of days while waiting for results. He didn't make his Grapefruit League debut until March 15, finishing with eight total innings across three starts and reaching 61 pitches in his final outing. Nos. 1-3 starters Sandy Alcantara, Pablo López and Elieser Hernandez appeared in a game setting six times in the spring.

In order to continue his throwing progression, MLB Pipeline's No. 15 overall prospect was optioned to Triple-A Jacksonville rather than be rushed into the Opening Day rotation. Scheduled to throw five innings or 75 pitches in the sim game, he instead exited as an extra precaution following two-plus frames. Before this latest development, the plan called for him to get one more outing at the alternate training site, and then rejoin the club during its first road trip to New York and Atlanta that runs from April 8-15.

Miami elected to begin the season with a four-man rotation (Alcantara, López, Hernandez and Trevor Rogers) with two off-days in the first nine dates of the schedule. The extra spot was assigned to the bullpen. When the Marlins need a fifth starter on that trip, No. 12 prospect Nick Neidert is an option, as he piggybacked off Sánchez's outings in the spring. So are rookie left-handers Daniel Castano and Braxton Garrett.

"Those are conversations about the start that's going to be coming up -- I think it's in New York -- [concerning] who do we want to start that game and who do we think's the best guy for that," Mattingly said. "So we've been talking through that a little bit. I don't think we came to a final decision. We've got guys lined up, multiple guys lined up for that start, so I feel like we're in pretty good shape as far as having a guy ready and available for that."

The Marlins will not rush Sánchez, who had been eased into a spring routine in his first two years with the organization. As a Minor Leaguer in the Phillies' system, he spent time in 2018 on the injured list with right elbow inflammation. With the return of a 162-game season in 2021, Sánchez will have an innings limit of around 165. His single-season career high is 114 innings between two Minors levels in '19. Despite that, the Marlins have a plan in place for him to pitch into September.

Sánchez went 3-2 with a 3.46 ERA in seven regular season starts after his callup last season, and he went 0-1 in two postseason starts.