Another day, another Marlins prospect makes his MLB debut.

On Saturday, it was Daniel Castano's turn. The left-hander became the ninth Miami player to appear in his first big league game this season.

With so much roster turnover, the Marlins have been willing to give prospects with limited or no Double-A experience a shot in the big leagues.

Still, the organization is hesitant to rush right-hander Sixto Sánchez, its No. 1 prospect and the 24th-ranked prospect on MLB Pipeline’s Top 100 list.

Sánchez is on the 40-man roster and the Marlins have made it clear they will promote him, but not until he is fully ready, meaning he is built up in terms of innings as well as his pitch count.

Working at the club’s alternate training site in Jupiter, Fla., Sánchez is currently built up to throw three innings in scrimmages. The Marlins would like to see him get to at least five innings before giving serious consideration to bringing him to the big leagues.

“Sixto has been good,” manager Don Mattingly said on a Zoom call Saturday. “That’s really what it’s been, making sure that he’s being built up properly. I feel pretty confident that there is going to be a time this year that we see Sixto. It just hasn’t been yet.”

So why is Sánchez behind some others in the system?

It goes back to Spring Training, when the right-hander was brought along slowly. By his own admission, he wasn’t in his best playing shape, and the team didn’t use him in any Grapefruit League games, ramping up his throwing program after the rest of the other pitchers.

In 2019, Sánchez spent most of the season at Double-A Jacksonville, save for two early starts at Class A Advanced Jupiter, and he logged 114 total innings with a 2.76 ERA.

Considered potentially the ace of the future, Sánchez still is a comparatively young prospect -- he turned 22 on July 29.

He dealt with right elbow inflammation while in the Phillies' system in 2017, so the Marlins have been extremely careful with Sánchez.

He’s fully healthy, but he hasn’t logged more than 114 innings in a season in a Minor League career that started in 2015.

“Our No. 1 [thing] is always going to be health,” Mattingly said. “You’re talking about building a guy up and making sure that he’s properly ready, because guys like him, they come up here and want to show you what they have.”

Sánchez has a 100-plus mph fastball.

“They may try to do a little more than what they probably should do,” Mattingly noted. “You want to make sure they’re ready to show it all, and their arm is ready for it. That’s the biggest thing.”

Off to a hot start, the Marlins are going to give themselves every opportunity to make the playoffs.

So, in late August or September, if they feel Sánchez is ready, then he likely will join Miami’s long list of players making their MLB debuts in 2020.

“Usually guys like Sixto, they don’t go bouncing back and forth,” said Mattingly, meaning up and down from the Majors to the Minors. “Once you see him, you’re like, ‘OK, we can do something with that.’ You want to make sure that guy is ready, and he doesn’t come up here not prepared to physically compete.”

Mejía optioned, Bleier to IL
The Marlins made some roster moves on Saturday, optioning right-hander Humberto Mejía to their alternate training site. Mejía will still be staying with the club, as he is joining the five-man taxi squad.

The move was anticipated because Mejía pitched Friday in a sharp MLB debut, and he wouldn’t be available for at least five days. So it was a chance to add more bullpen help.

The Marlins also have scheduled off-days Monday and Thursday, and Mattingly said Mejía is a candidate to rejoin the rotation when needed.

Also, left-handed reliever Richard Bleier was placed on the 10-day injured list with a left triceps strain. He is expected to miss about two weeks.

Left-handed reliever Brian Moran was recalled from the taxi squad, and Miami selected the contract of switch-pitcher Pat Venditte.