The Mets’ infield plans for next year are already under assault.

Ronny Mauricio was expected to belong to that mix as a competitor for the third-base job but will undergo surgery instead, the team announced Tuesday, after he was diagnosed with a torn anterior cruciate ligament in his right knee.

The 22-year-old infielder sustained the injury in a Dominican Winter League game.

The Mets released a statement saying a timeline for Mauricio’s return will be given once he undergoes the procedure.

But it can be expected that recovery and rehab will cost him a significant chunk, if not all, of next season.

Last week at the winter meetings, president of baseball operations David Stearns said the club wasn’t seeking external options at third base and would let Mauricio, Brett Baty and Mark Vientos battle for the job in spring training.

Mauricio has played third base sparingly in his career and was receiving further repetitions at the position this winter in the Dominican.

Mauricio spent most of last season at Triple-A Syracuse before debuting with the Mets in September. In 26 games for the team, he owned a .248/.296/.347 slash line with two homers, nine RBIs and seven stolen bases.

Team officials have been intrigued by his raw power and athleticism even as they searched for a spot for him defensively.

Developed as a shortstop, Mauricio began playing second base and left field last season for Syracuse before getting a taste of third base with the Mets.

His tape measure home runs in spring training last season turned him into a sensation with the fans.

Mauricio fell Sunday while taking a secondary lead off first base for Licey in the Dominican league.

It marks the second straight season a Mets player was injured while away from the team.

Last March, closer Edwin Diaz tore the patellar tendon in his right knee during an on-field celebration with Team Puerto Rico at the World Baseball Classic in Miami and underwent surgery that cost him the entire season.

If there is a silver lining this time, the Mets still have time to pivot if they decide to look externally for another third-base option.

Former Mets infielder Justin Turner is among the available names on the market and might not command a commitment beyond one year.

Matt Chapman is the top free-agent third baseman, but would likely require a significant commitment.

The Mets could also hold steady with Baty, who struggled as the primary third baseman last season and was demoted to Syracuse in August before returning for the final month.

Baty, 24, produced a .212/.275/.323 slash line with nine homers and 34 RBIs in 108 games. He was also shaky defensively, but has been working out this winter with Francisco Lindor in an effort to get a jump on spring training.

The Mets also have Vientos, who will have to show he’s capable of handling the position defensively as the team looks to maximize his power potential.

Vientos has appeared better suited as a DH/first base possibility.

Another possibility is veteran Joey Wendle, who arrived last month on a one-year contract worth $2 million to provide coverage at multiple infield positions.

But Stearns’ inclination before Mauricio’s injury was to give the kids first dibs at third base.

“I think it is important for us as an organization to learn about our younger players and to provide them with opportunity at the major league level,” Stearns said at the winter meetings. “That doesn’t have to be all on Opening Day, but over the course of the year we’ve got to learn about these guys.”