CINCINNATI — For a third time this season the Mets are promoting a highly regarded starting pitcher with the hope of improving the rotation.

Brandon Sproat, who began the year as the organization’s top pitching prospect, will be called up from Triple-A Syracuse to pitch Sunday against the Reds, sources confirmed on Thursday.

Sproat, who turns 25 in two weeks, will join a rotation that includes Nolan McLean and Jonah Tong, both of whom have debuted for the club in recent weeks. Sproat’s promotion coincides with veterans struggling in the starting rotation, most notably Kodai Senga and Sean Manaea.

New York Mets pitcher Brandon Sproat pitching.Brandon Sproat will start Sunday against the Reds. Corey Sipkin for the NY POST

Sproat has thrived for Syracuse in the second half, pitching to a 2.59 ERA in his last 11 starts after a rough 2 ½ months to begin the season.

The Mets are looking for answers as they seek to, at minimum, secure a National League wild-card berth over these final 22 games, if not catch the Phillies for first place in the NL East. Beyond that, the Mets are auditioning pitchers for a potential postseason rotation. Though Sproat is not yet on the 40-man roster he would be eligible for postseason participation given that he was in the organization before Sept. 1.

Still to be resolved is a next step for Senga, who is expected to inform team brass by Friday if he’s willing to accept a minor league assignment as the Mets attempt to get him back on track. Senga’s contract stipulates that he must give his consent for such a move.

Brandon Sproat, New York Mets pitcher, at spring training.Brandon Sproat is being called up for his debut. Corey Sipkin for the NY POST

As it stands, the Mets have David Peterson, Tong and Sproat aligned to face the Reds this weekend. Team officials had originally been leaning toward McLean for the series finale, but it’s now probable he will open the Mets’ four-game set that begins Monday in Philadelphia. Manaea had been told he is pitching Monday, but it’s possible the left-hander will now move back a day.

Sproat has a familiarity with the Mets after spending much of spring training with the team. He and McLean formed a tight bond at Syracuse.

McLean recently told The Post the key to Sproat’s turnaround this season after a rough stretch has been controlling the count better.

“He was getting behind on counts, and when you do that, it’s so much harder to get guys out,” McLean said. “He’s done just a better job of getting ahead of guys, and then he’s got such good pitches as soon as he gets ahead.”