PORT ST. LUCIE, Fla. -- More than perhaps any other player, the Mets are counting on Amed Rosario to take a significant step forward this season, play a full year and blossom into one of the game’s top young shortstops. So they held their collective breath when Rosario departed Monday’s 9-3 loss to the Red Sox in the fifth inning, after being struck on the left hand by a pitch.

Then they breathed a collective sigh of relief when X-rays came back negative. Rosario is day-to-day, and will return to the lineup as soon as the swelling on the outer region of his hand subsides.

“I’m happy because it wasn’t something bad,” Rosario said through an interpreter. “To be honest, I don’t really have a lot of pain. It’s just a little bit tight right now.”

Leading off the bottom of the fifth, Rosario took a Mike Shawaryn pitch off his hand and immediately left the game. Andres Gimenez replaced him on the basepaths, and eventually at shortstop.

“It’s always scary when one of your guys gets hit,” manager Mickey Callaway said. “You don’t want anyone to get injured.”

It was particularly frightening for the Mets considering the state of the left side of their infield. The team is already playing without third basemen Jed Lowrie (sprained left knee capsule) and Todd Frazier (strained left oblique), prompting the Mets to use their primary backup shortstop, Adeiny Hechavarria, more frequently at third.

Besides Rosario, the only healthy player on the 40-man roster with significant shortstop experience is Luis Guillorme. Non-roster candidates include Gimenez, a 20-year-old prospect who is not quite big league-ready, and veteran Danny Espinosa.

On top of all that, Rosario was enjoying a torrid spring, batting .462 with a home run and two doubles in five games. He hopes to add to those totals as soon as he heals.

“I feel great,” Rosario said. “I feel a lot more confident now.”