With three starting pitchers on the injured list since the first weekend of the regular season, patching the rotation together has been a challenge for Marlins manager Don Mattingly.

There finally are encouraging signs that the club’s ace, Sandy Alcantara, could be less than a week away from returning.

The 24-year-old right-hander threw a 22-pitch bullpen session Saturday, and he is scheduled to throw about 50 pitches on Wednesday. If that goes well, it will be up to the organization to determine if Alcantara is ready to rejoin the rotation.

“I feel like 100 percent ready to go right now,” Alcantara said on a Zoom call on Tuesday. “I’m just waiting for the call. I threw a bullpen three days ago, and my arm feels good. Let’s see what happens after that.”

Alcantara, left-hander Caleb Smith and righty José Ureña were among the 18 Miami players to test positive for COVID-19 in late July.

Miami’s Opening Day starter, Alcantara impressed in his lone appearance, limiting the Phillies to two runs (one earned) on three hits while striking out seven in 6 2/3 innings in a win.

“Everybody is on a little different program or timetable, depending on how they’re feeling since they came back,” Mattingly said. "Sandy has thrown a ‘pen. He’s going to throw live BP Wednesday.”

Mattingly noted the players on the COVID-19 injured list are working separately from the other players at Miami’s alternate training site at the Roger Dean Chevrolet Stadium complex in Jupiter, Fla.

“José and Smitty are close behind,” Mattingly said of his other top starters.

The constants in the rotation have been right-handers Pablo López and Elieser Hernandez.

On Monday night, right-hander Jordan Yamamoto was optioned to the alternate training site, and rookie Humberto Mejía made his second big league start on Tuesday.

Even without 60 percent of their Opening Day rotation, the Marlins have gotten off to a solid start to put themselves in contention.

Miggy close to ready
Of the 18 players on the COVID-19 injured list, the position player closest to returning is shortstop Miguel Rojas. The unofficial captain of the squad, Rojas played in the first three games before testing positive for the coronavirus. He was off to a hot start, batting .700 with a home run and five RBIs.

Mattingly said the position players will get about 25-30 at-bats in either live bullpen sessions, simulated games or scrimmages before being reinstated.

Series of roster moves
Miami had a busy day on Tuesday making roster moves. Mejía was recalled, and outfielder Corey Dickerson was activated from the bereavement list.

The Marlins also placed left-hander Brian Moran on the 10-day injured list with right knee patellar tendinitis. Right-hander Mike Morin was placed on the 45-day injured list, and Miami optioned right-hander Justin Shafer to the alternate training site.

The club also selected the contracts of right-hander Brett Eibner and lefty Brandon Leibrandt from the alternate training site.

Leibrandt, a sixth-round Draft pick of the Phillies in 2014, went to Florida State. He missed 2019 as he recovered from Tommy John surgery.

Leibrandt is the son of former big league pitcher Charlie Leibrandt, who pitched from 1979-93 and was part of the Royals' 1985 World Series title team.

Mattingly, who faced Charlie Leibrandt in his playing days, told Brandon that he resembles his father in looks and how he pitches.

“They look alike,” Mattingly said. “I told him when I was able to say hello that he looked like his dad.

“I remember [Charlie] more from Kansas City when he first came up. He was a guy who was a lot to deal with. Just a number of pitches. A guy that located, was not giving in. Not an overpowering guy, but a guy who made you work to get [a pitch to hit].”

Impressed with Díaz
The intention from the start was for first-base prospect Lewin Díaz to be with the club for three days, or until Dickerson came off the bereavement list.

The Marlins optioned Díaz after Monday’s game, after the left-handed-hitting first baseman went 2-for-8 with an RBI, a walk and a strikeout.

Miami’s No. 8 prospect, according to MLB Pipeline, Díaz projects to have a bright future with the organization.

“He looked comfortable,” Mattingly said. “He didn’t look jumpy. I liked what I was able to see. It gives me more confidence moving forward with him.

“We knew it was going to be a three-day thing. It was going to be a short sample right now. This is a kid that we like a lot, and he is going to be part of where we’re going."