Frazier went down with the injury after the Mets' 3-3 tie with the Houston Astros on Monday at FITTEAM Ballpark of the Palm Beaches in West Palm Beach, Fla.
"I was hitting the ball great and just at the end I just felt a little tightness on my left side," Frazier told reporters Tuesday. "It's classified as a strain in my left oblique."
Frazier said he has never had the injury and is frustrated about the setback.
"It's not the best start, but luckily it happened here in spring training and we can nip this thing in the bud and get ready for the season," Frazier said.
A team source told MLB.com that Frazier's strain "doesn't appear to be severe." He will have a cortisone injection in New York and there is no timetable for his return.
Frazier, 33, never went on the disabled list during the first seven seasons of his career. He landed on the disabled list twice last season. The two-time All-Star hit .213 with 18 home runs and 59 RBIs in 115 games in 2018 for the Mets. Frazier joined the Mets in February 2018 as a free agent. He is a free agent again next offseason.
The Mets continue their spring training slate with a game against the Atlanta Braves at 1:05 p.m. on Tuesday at Champion Stadium in Orlando. New York gets the 2019 season start against the Washington Nationals on March 28 at Nationals Park in Washington, D.C.