MIAMI -- Marlins top prospect Sixto Sánchez will not be in the Opening Day rotation, a source told MLB.com on Monday. He will be optioned to Miami's alternate training site, which is in Jacksonville, home of the club's Triple-A affiliate. Considering the 22-year-old right-hander was delayed pitching in Spring Training games, it shouldn't come as a surprise.

The club has not confirmed the move.

Following his third and final Grapefruit League outing on Thursday night, Sánchez acknowledged he needed just a little more time to be ready for the season. MLB Pipeline's No. 15 overall prospect reached 61 pitches across 3 1/3 innings in that start, facing most of the Nationals' expected Opening Day lineup. He was scheduled to throw again in some capacity on Tuesday.

Sánchez didn't make his Grapefruit League debut until March 15, and he finished with eight total innings. He allowed one run on five hits with two walks, one hit batter and three strikeouts, compiling a 1.13 ERA, 0.88 WHIP and .185 batting average against.

The Marlins had consistently stated they want Sánchez to be built to at least 75 pitches or five innings before starting a regular-season game. Right-handers Sandy Alcantara, Pablo López and Elieser Hernandez threw in a game setting six times this spring -- the last being a tuneup. Southpaw Trevor Rogers, who also got a late start at camp, had five outings under his belt.

Miami will not rush Sánchez, who had been eased into a spring routine his first two years with the organization. With the return of a 162-game season in 2021, he will have an innings limit. Despite that, the Marlins have a plan in place for the flamethrower to pitch into September. His single-season career high is 114 innings in '19.

"We're going to keep building him, and it's one of the things that we're going to make sure we do it safely," Marlins manager Don Mattingly had said during a Zoom call last week. "I'm assuming that he's going to come out of this fine, and make sure -- with Sixto, we always talk about we would give him the extra day if he needed it. He hasn't needed it to this point. He's building and seems to be effective. So, we just kind of read the situation with him and then go from there."

Sánchez, who entered Spring Training projected to make the Opening Day rotation, was delayed getting to camp from the Dominican Republic because of visa issues. He also had a false COVID-19 positive test that set him back a couple of days while waiting for results. Sánchez went 3-2 with a 3.46 ERA in seven regular-season starts after his callup last season.

With a source telling MLB.com that Rule 5 Draft selections Paul Campbell and Zach Pop are making the club, that may tip Miami’s hand as to how many starting pitchers will open the season. With two off-days within the first nine dates on the schedule, the rotation is likely to go with four members, with the extra spot assigned to the bullpen.

If that's the case, it's between Rogers and right-hander Nick Neidert, Miami's Nos. 7 and 12 prospects, respectively, for the fourth rotation spot. Entering Monday, Rogers had recorded the second-most strikeouts in Spring Training. Neidert had been coming on in relief of Sánchez's starts this spring.