Highly regarded New York Mets pitching prospect Jenrry Mejia appears headed for Tommy John surgery that will sideline him for a year.

The 21-year-old Mejia, who made the Opening Day roster last season as a reliever, has a complete tear of the medial collateral ligament in his right elbow, the team announced. Mejia was examined Monday in New York by Mets doctor David Altchek, who recommended surgery. Mejia plans to get a second opinion from Dr. James Andrews in Birmingham, Ala., before proceeding.

Mejia departed after four innings Friday in his latest start for Triple-A Buffalo, although his pitch count was already at 81 (with 39 pitches in the first inning) and there were no outward signs of trouble.

“I felt a little pain on one pitch … late in the game, in the fourth inning,” Mejia said Monday after rejoining the Mets’ Triple-A Buffalo affiliate following an examination in New York.

The staff was unaware until Mejia came to the ballpark between starts with swelling in his forearm.

“He never mentioned it after the game or anything. I think this is just something that happened probably near the end of his last outing, but he’s a tough kid,” Triple-A manager Tim Teufel said. “He probably didn’t even know he hurt himself.

“In between starts he just complained that his forearm was kind of swollen a little bit. And so we checked into it. [Trainer] Joe Golia recommended for him to get checked out and have an MRI done. Of course, they had him flown into New York. The bad news came out today that he’s got some major issues in his elbow that he needs to take care.”

Mejia had been 1-2 with a 2.86 ERA and 21 strikeouts in 28 1/3 innings in the International League. The Buffalo staff had praised the development of Mejia’s curveball and changeup this year, which was the key to him returning to the major league level as a starting pitcher.

“It is what it is,” Mejia said about the injury. “Something happened for whatever reason.”