PORT ST. LUCIE — The biggest question at Mets camp soon will surround the players no longer at Mets camp. 

Nine players on their 40-man roster — including their entire starting infield — can participate in the World Baseball Classic that begins Wednesday.

Every team will have concerns about its players thrown into intense, international competition after a few weeks of ramping up, but few teams are better represented than the Mets. 

On Saturday, Mets manager Buck Showalter chatted with Team USA manager Mark DeRosa and delivered a message: “Make sure they all come back healthy.” 

Pete Alonso, Jeff McNeil, Adam Ottavino and Brooks Raley have left Mets camp to play for the United States.

Also set to represent their home countries are Edwin Diaz and Francisco Lindor (Puerto Rico), and Eduardo Escobar and Omar Narvaez (Venezuela).

Francisco Lindor has left Mets camp to play for Puerto Rico in the World Baseball Classic.
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Elieser Hernandez is part of Venezuela’s designated pitcher pool. 

Several who are not on the 40-man roster will be playing in the tournament, too.

As other clubs hold rounds of cuts to trim major league camp, the Mets may be seeking additional bodies. 

There are some health-conscious agreements in place — Diaz will not pitch on consecutive days — but players who are accustomed to slowly building up strength through camp instead could be going all-out for the glory of their homeland. 

Here are more questions the Mets face after their first off day of the Grapefruit League season on Monday, which came two weeks after their first full-squad workout: 

Can this rotation hold up? 

After a few weeks of camp, a 34-year-old and 27-year-old have encountered health issues.

The other top options for the Mets’ rotation — aged 40, 38, 35, 30 and 27 — are still standing. 

A rotation this old was always going to be a concern.

Jose Quintana suffered a small stress fracture on his fifth rib on his left side, the Mets said Monday, a day after he reported side tightness.

The team has not released a timetable yet for his return.

David Peterson, a depth piece, took a comebacker off his left foot Saturday and appears to have avoided the worst, sustaining a contusion and listed as day-to-day. 

Justin Verlander is entering his age-40 season with the Mets.
Justin Verlander is entering his age-40 season with the Mets.
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Justin Verlander, Max Scherzer and Carlos Carrasco enter the season with a combined 45 years of major league experience.

Kodai Senga, who debuted in the exhibition season Sunday, is technically a rookie but has plenty of innings on his arm.

The Mets will have to test their rotation depth — and likely early. 

On the outskirts of the rotation are Peterson and Tylor Megill.

Among the next batch are Hernandez and Joey Lucchesi, who is building up in his first season since Tommy John surgery. 

Can a kid crack the roster? 

Probably not, but they are pleading their cases.

Brett Baty has the most realistic shot, his loud bat threatening Escobar’s reign at third base.

But the 23-year-old has shown a shaky glove, too, and Showalter repeatedly has stated the Mets will value defense heavily.

Mets prospect Brett Baty has impressed with his bat but has had problems defensively.
Mets prospect Brett Baty has impressed with his bat but has had problems defensively.
Corey Sipkin for the NY Post

Baty, who has opened 8-for-17 with a home run in the Grapefruit League, likely will need to crush Triple-A pitching, too, for a call-up. 

Ronny Mauricio and Mark Vientos are having similarly sizzling springs and present other defensive concerns.

Mauricio, a shortstop, will have to learn another position (perhaps second or third base and maybe an outfield spot) in the minors.

Vientos, a corner infielder, needs to prove his glove is not a liability. 

Vientos reached the majors late last season as a righty-hitting designated hitter, and that spot could open again.

Darin Ruf, who struggled with the Mets last season, has yet to debut because of a wrist issue. 

Who wins the final bullpen spots? 

Diaz, Ottavino, Raley, David Robertson and Drew Smith have jobs locked up.

Stephen Nogosek (who is out of options) and Zach Greene (a Rule 5 pick who would be offered back to the Yankees if he doesn’t make the team) are front-runners for the Opening Day bullpen because they likely would be lost otherwise. 

That leaves one spot open from a group that includes Jeff Brigham, Sam Coonrod, John Curtiss, Bryce Montes de Oca and Stephen Ridings.

All have flashed good stuff, and all can be optioned to the minors. 

It is also possible the Mets carry Hernandez or Lucchesi as a long man. 

Finding Nimmo (& Marte) 

Two of the Mets’ three outfielders have yet to debut in the exhibition season, though concern seems low for both. 

Brandon Nimmo is taking it slow in what can be a long spring training.

Starling Marte is expected to get his first taste of the Grapefruit League this week after offseason surgery on both groins.