New York Mets starting pitcher Kodai Senga had a platelet-rich plasma injection in his ailing right shoulder and won't throw for at least three weeks, all but sealing that he won't take the mound as the team's Opening Day starter.

Manager Carlos Mendoza told reporters Sunday that Senga had returned to spring training camp in Port St. Lucie, Florida, after traveling to New York for diagnosis and treatment.

The 31-year-old Senga was diagnosed with a moderate posterior capsule strain in his pitching shoulder after an MRI on Wednesday. Mendoza said the hope is the shot will accelerate the healing.

"Let the shot do the work, and once we start ramping up his throwing program, we'll have a better idea how he's bouncing back and all that," Mendoza said. "We got to let it heal."

Once doctors give him the green light to throw, Senga still will need the time he would have had in spring training to prepare for the regular season, meaning he likely will be on the injured list when the Mets open the season March 28 at home against the Milwaukee Brewers.

The Mets had the MRI performed after Senga reported shoulder fatigue following his bullpen sessions in spring training.

Senga was an All-Star and finished second in National League Rookie of the Year voting last year after going 12-7 with a 2.98 ERA in 29 starts. He threw 166 innings. Prior to joining the Mets, he pitched 1,340 innings across 11 seasons in Japan.

Entering the second season of a five-year, $75 million contract he signed with the Mets in December 2022, Senga is expected to anchor a rotation that includes Jose Quintana, Luis Severino, Sean Manaea and Adrian Houser.