NEW YORK -- Mets pitcher Kodai Senga felt tightness in his right triceps during a minor league rehab outing and won't pitch during the regular season.

Mets manager Carlos Mendoza said Sunday the 31-year-old right-hander might throw a bullpen session and remains a possibility for the postseason.

Senga pitched a hitless inning with a walk and two strikeouts for Triple-A Syracuse on Saturday night in his first rehab outing since straining his left calf in his season debut on July 26. He threw eight of 15 pitches for strikes.

"He felt like he could continue to pitch, but he just wanted to play it safe," Mendoza said. "It's been a hard year for him. He's worked his tail off. You feel for him. Every time he wants to push it and he wants to take the baseball, then he's dealing with something. Hopefully this is nothing serious but it's going to set him back a little bit as far as game competition at the big league level."

Senga joined the Mets ahead of the 2023 season for a $75 million, five-year contract and became an All-Star in his first season. He went 12-7 with a 2.98 ERA in 29 starts and finished second in NL Rookie of the Year voting.

Mets president of baseball operations David Stearns said Feb. 15 an MRI revealed a capsule strain in the pitching shoulder, a scan performed after Senga twice expressed having shoulder fatigue following throwing sessions.

Senga made four minor league rehab starts from July 3-20. He allowed two runs and two hits over 5 innings against Atlanta on July, leaving with the calf strain after his 102nd pitch. Senga struck out nine and retired his last 10 batters.

"He's a competitor and he knows that we are a better team if he's healthy," Mendoza said. "He's going to continue to try everything that he can in his power to be available for us."