PORT ST. LUCIE — Just over a week into spring training the Mets have concern about a key player’s health.

Kodai Senga was absent from workouts Wednesday after incurring arm fatigue following a bullpen session the previous day, according to manager Carlos Mendoza.

The right-hander was to be evaluated by the Mets’ training staff; it wasn’t immediately known if Senga would receive an MRI exam.

“He got on the mound [Tuesday] and today he came in and it was overall arm fatigue,” Mendoza said following the team’s workout.

Senga avoided the injured list last season, when he arrived on a five-year contract worth $75 million.

At the time of his signing there was some level of concern with his elbow following a physical.

But Senga started 29 games for the Mets last season and recorded 202 strikeouts over 166 ¹/₃ innings with a 2.98 ERA to finish second in the NL Rookie of the Year voting.

The Mets mostly pitched Senga on extra rest last season to ensure he wouldn’t be overtaxed in adjusting from Japan, where starting pitchers work only once in a week.

The Mets have pitching depth in Tylor Megill, Jose Butto and Joey Lucchesi, among others, but Senga would be difficult to replace in a rotation filled with question marks.

It’s a group behind Senga that consists of Luis Severino, Jose Quintana, Sean Manaea and Adrian Houser.

Another piece of the team’s rotation depth, David Peterson, underwent offseason surgery to repair a torn hip labrum and will likely miss at least one to two months to begin the season.

“The biggest thing we have in the conversations with our players is they need to get ready for their season,” Mendoza said. “Is that New York on March 28? We’ll see. If we’re having those tough conversations it means everyone is healthy, everyone is throwing the ball well. They want to force us to make those decisions.”

If Senga’s situation is serious enough to sideline him for an extended stretch, there is starting pitching still available on the free-agent market: most notably Blake Snell and Jordan Montgomery, both of whom are represented by Scott Boras.

But it’s also possible the Mets would stick to their offseason plan of avoiding big expenditures as they look to evaluate from within the organization.

Team officials heavily courted Japanese ace Yoshinobu Yamamoto in the offseason, but the right-hander was a special case in that he’s only 25 years old.

Yamamoto accepted $325 million from the Dodgers, a sum the Mets had offered.

The Mets have dealt with spring training health woes the last two seasons.

Last year, Edwin Diaz underwent surgery to repair the patellar tendon in his right knee after tearing it during a celebration at the World Baseball Classic. Diaz missed the season.

Also last spring, Jose Quintana underwent rib surgery that kept him out until after the All-Star break.

In 2022, Jacob deGrom had elbow discomfort following his first Grapefruit League appearance and didn’t pitch again for the team until August.

Senga arrived at camp vowing for improvement after his strong rookie season.

His plans have included the incorporation of a slider — a pitch he threw sparingly last season after learning it from Max Scherzer and Justin Verlander.

“It’s something I am working on, so whether it’s good or bad I will use it in [spring training] and see how the hitters look against it,” Senga told The Post this week. “I just want to add another weapon to my repertoire and hopefully I can add to it.”