Mets right-hander Kodai Senga missed a planned bullpen session on Sunday due to "triceps tightness," manager Carlos Mendoza said on Monday.

Six days after Senga told the team he needed more time to be ready for a rehab stint because his mechanics were off, he experienced tightness and will target another day later in the week, Mendoza said.

"Went out and played catch, soft-toss," Mendoza said. "Hopefully he throws again (Tuesday) and we're in a bullpen by the end of the week."

An All-Star in 2023, Senga is on the injured list with a right shoulder capsule strain. Mendoza has referred to him as "meticulous" in his approach, which currently is focused on what Senga said was getting all of his power coming toward the plate.

On April 10, Senga was transferred to the 60-day injured list.

He threw live batting practice April 29 and May 4 but backed off his planned upramp and return from the injured list with his earliest potential return on Memorial Day (May 27).

That timeline is seemingly invalid, although Mendoza called the postponed bullpen session on Monday a "low-level concern."

"I wasn't able to deliver 100 pecent of it toward the catcher, which is very important," Senga said in early May. "When that is happening, I'm more susceptible to getting hit and also more susceptible to injuries if that continues."

Senga was an 11-year pro in Japan before agreeing to a five-year, $75 million contract with the Mets in 2022.

He was 12-7 with a 2.98 ERA and 202 strikeouts in 166 1/3 innings last season.