Frankie Montas is out, setting the stage for the Mets to unveil a top pitching prospect on Saturday.

According to sources, Nolan McLean and Brandon Sproat are now considered the leading choices for that position. This comes after Montas was moved to the bullpen on Tuesday due to a series of disappointing outings.

In recent days, multiple club sources indicated McLean was ahead of Sproat in the pecking order. But before Tuesday’s game, manager Carlos Mendoza wasn’t prepared to announce the selection.

Mendoza ruled out Paul Blackburn, who is scheduled for another rehab start Wednesday with Triple-A Syracuse, removing him from the mix.

“Whoever comes up here, if it’s one of the prospects, the plan is to give them a good look here,” Mendoza said before his team faced the Braves at Citi Field.

McLean last pitched Sunday for Syracuse and would be on five days of rest if he’s called up for his major league debut. The right-hander has pitched to a 2.78 ERA in 16 appearances this season for Syracuse after beginning the year at Double-A Binghamton. McLean, 24, has struck out 97 in 87 ¹/₃ innings for Syracuse.

Sproat began the season slowly but has emerged as a factor in recent weeks. The right-hander has pitched to a 4.10 ERA in 22 starts overall. Sproat, 25, last pitched Thursday for Syracuse.

“There is a lot to like, especially where they are at with their development,” Mendoza said. “We continue to ask a lot, whether it’s Sproat with the changeup or finding something against lefties. The same thing with McLean, but the way they have been competing, they have been going more than five innings and getting results. Everything we are asking them to do we continue to do it.”

The Mets promoted 22-year-old stud pitching prospect Jonah Tong to Syracuse on Sunday — after he dominated at Double-A Binghamton with a 1.59 ERA over 20 starts — but the expectation within the organization is the right-hander won’t be a candidate to pitch in the major leagues this season.

Montas threw 72 pitches over three innings in his appearance Saturday behind an opener in Milwaukee and allowed three runs, two of which were unearned. The right-hander overall has disappointed, pitching to a 6.38 ERA in eight appearances for the club.

Montas arrived last winter on a two-year contract worth $34 million that contains an opt-out after this season.

“Right now, he will be that long guy [in the bullpen], but you never know,” Mendoza said. “That’s what I told him, too. He could be pitching the eighth inning in a tie ballgame because of where we are bullpen-wise. It’s something that he has never done, so it will be fluid. But what I told him is he’s got to be honest with us, too. If he needs an extra day, he’s got to let us know. The recovery time and how much we’re going to use him is still fluid.”

The Mets could use length from a starter. Entering Tuesday’s game no starter other than David Peterson had pitched at least six innings since Clay Holmes on June 7.

In getting swept three games at Milwaukee, neither Kodai Senga nor Sean Manaea lasted even five innings, sandwiched around Montas’ short performance behind opener Reed Garrett.

“Everyone is different, but I think [length] starts with attacking hitters and staying on the attack, avoiding deep counts,” Mendoza said. “If you get ahead 0-2 and before you know it it’s 3-2 and it’s a seven or eight pitch at-bat, and you look up and it’s the fourth inning and it’s 80 pitches or something and it’s the fifth inning and it’s 85, 90, I think it’s just understanding this and we have done that at times. It’s been a struggle for the past six weeks or so.”