NEW YORK -- Noah Syndergaard left his start for the New York Mets with a hamstring injury in the seventh inning of Saturday night's game against the St. Louis Cardinals.

Syndergaard reached for his right hamstring after throwing a pitch. Mets manager Mickey Callaway and an athletic trainer went out to check on Syndergaard, who quickly walked off the field with a bit of a limp. He was later diagnosed with a strain and will be re-evaluated Sunday morning, Callaway said.

Robert Gsellman entered with New York leading 8-3. St. Louis scored three runs before the inning was over. The Mets held on to win 8-7.

Mets pitcher Noah Syndergaard walks off the field with head trainer Brian Chicklo in the seventh inning Saturday night against the Cardinals at Citi Field. Mike Stobe/Getty Images

"It was on that one pitch," Callaway said. "That deep in the game, if he feels anything, you get him out with a five-run lead."

Syndergaard threw 102 pitches. He was charged with five runs, four earned, and six hits in six-plus innings.

Syndergaard did not talk to reporters after the game.

"We really have no idea at this point," about the extent of the injury, Callaway said.

Earlier in the game, plate umpire Brian O'Nora left after getting hit in the groin by a foul ball. Matt Carpenter fouled off a pitch from Syndergaard in the third inning, and the ball bounced up and hit O'Nora. He staggered but stayed on his feet, and was checked by a Mets athletic trainer.

O'Nora, 56, initially remained in the game following a brief pause to gather himself. But a few pitches later, with Dexter Fowler at the plate, the veteran ump headed for the Mets' dugout in discomfort with his hand covering his mouth.

In April 2013, an intestinal tear forced O'Nora to make a sudden exit from a Phillies-Mets game at Citi Field.

The Associated Press contributed to this report.