NEW YORK — Todd Frazier’s frustrating first season with the New York Mets just hit another snag.

The affable third baseman was placed on the 10-day disabled list Monday with a strained muscle in his left rib cage. It’s the second DL stint for Frazier since joining the struggling Mets. The 32-year-old slugger had never been on the disabled list before 2018.

Frazier said he felt some discomfort his first time up Sunday against Tampa Bay and it got progressively worse as the game went on. He had an MRI and received a cortisone shot, but it’s unclear how long he’ll be out.

“It’s not fun at all. It’s something I never thought would happen,” Frazier said. “Maybe a DL stint, but, you know, the older I get I still feel like I’m in control of my body and then something like this happens. So it’s unfortunate, it stinks, but there’s nothing else I can do about it. Just keep on trying to get better and hopefully this isn’t a long ordeal.”

New York manager Mickey Callaway called Frazier’s injury a mild strain.

A two-time All-Star, Frazier signed a $17 million, two-year contract with the Mets as a free agent in February. He is batting .217 with 10 homers, 32 RBIs and a .685 OPS in 61 games. He was sidelined from May 8 to June 1 with a strained left hamstring.

“Just another little bump in the road,” Frazier said.

Jose Reyes played third base in the first game of Monday’s doubleheader against Philadelphia, with Ty Kelly set to start at the hot corner in the nightcap.

Beyond that, Callaway said the Mets were still figuring out how they plan to fill Frazier’s spot. Wilmer Flores is another option.

Slogging their way through an extremely disappointing season, the Mets also are missing injured outfielders Yoenis Cespedes and Jay Bruce from their projected starting lineup, as well as catcher Travis d’Arnaud.

“I know everybody works out hard, myself included, and these things happen — but they’re happening at a rapid pace,” Frazier said. “So maybe I need to change up what I’m doing in the offseason, or maybe I have to work out a little earlier or a little later, just depends. It’s something I’ll have to talk to these guys about.”

Right-hander Noah Syndergaard, sidelined since late May with a strained ligament in his index finger, could rejoin the rotation this weekend.

Left-hander Jason Vargas was scheduled to throw up to 80 pitches Monday night in a rehab outing for Class A Brooklyn and also could return to the big league rotation this weekend against Washington.

Right-hander Drew Gagnon will be called up from Triple-A Las Vegas to start Tuesday night against the Phillies, his major league debut. The 28-year-old Gagnon, who was in the Mets’ clubhouse Monday, is 1-4 with a 4.67 ERA in 17 starts at Las Vegas.

New York made a flurry of roster moves Monday. In addition to recalling Kelly and left-hander P.J. Conlon from Las Vegas, the team brought up right-handed reliever Jacob Rhame as the 26th man for the doubleheader. Right-hander Chris Flexen was optioned to Triple-A.

Flexen started Sunday’s 9-0 loss to the Rays and was tagged for five runs and five hits in three innings.