NEW YORK — Mets right-hander Kodai Senga was diagnosed with a Grade 1 hamstring strain Friday and will be reevaluated in two weeks, manager Carlos Mendoza said after the team’s 7-5 loss to the Tampa Bay Rays.

Senga, the Mets’ top starter this season, suffered the injury running to cover first base in the sixth inning of Thursday’s win against the Washington Nationals. He was placed on the injured list Friday morning, but the Mets didn’t know the extent of the setback until he was examined in the afternoon.

Mendoza called the development “relatively good news,” though he indicated Senga won’t return for at least a month.

“It depends on the player,” Mendoza said. “It’s two weeks of very little physical activity. Hopefully we keep the arm going, but he’s got to be symptom-free before we start ramping him up. So, could be four, five, six [weeks]. Who knows? But, again, it’s a low grade, which is good news.”

Senga’s brief major league career has been a blend of dominance and injury trouble. An 11-year veteran in Japan’s NPB, Senga signed with the Mets before the 2023 season and posted a 2.98 ERA in 29 starts to finish second in the National League Rookie of the Year voting. But he was shut down early in spring training in 2024 with a shoulder injury and missed much more time than expected. He didn’t make his season debut until July 26 and left the game in the sixth inning with a severe calf strain that sidelined him until the postseason.

This season, the 32-year-old Senga has been the best pitcher in a rotation with the best ERA across the majors. He exited Thursday’s game with a 1.47 ERA, the lowest mark in baseball.

Now the Mets are readying for another extended period without him.

“He wants to be involved in the process,” Mets president of baseball operations David Stearns said of Senga’s looming rehab. “And I think it’s important that we get on the same page as him from the jump. And that we’re all bought into what this process is going to look like. I think we got there last year, but any time you’re going through this multiple times, I certainly know Senga a lot better now than I did last year.

“Our medical staff has now worked through a rehab progression and a rehab process with him already on multiple occasions. So I think we feel pretty comfortable that whatever this turns out to be, we’re going to be able to work very productively with him to get him back healthy.”

For now, the Mets will slot veteran right-hander Paul Blackburn in Senga’s spot in the rotation. He is scheduled to start Wednesday against the Atlanta Braves.

Blackburn, who began the season on the injured list with knee inflammation, tossed five scoreless innings in his season debut on June 2 against the Los Angeles Dodgers before shifting to the bullpen for two appearances. He was charged with four runs in one-third of an inning of relief Friday against the Rays.

Sean Manaea and Frankie Montas, who are both currently on rehab assignments after beginning the season on the injured list, are possible options for the rotation in the near future.

Manaea is slated to make a third rehab start Sunday after recording 2 ⅔ scoreless innings for High-A Brooklyn on Tuesday. Montas, however, has struggled in his five rehab starts. The free-agent acquisition — he signed a two-year deal, $34 million contract during the offseason — had his worst outing Friday, giving up eight runs across just 1 ⅓ innings for Triple-A Syracuse. He owns a 13.17 ERA through the five starts, opening the door for him to possibly join the Mets as a reliever.