SAN FRANCISCO — Francisco Alvarez underwent surgery to repair the torn UCL in his left thumb on Tuesday. The Mets said it should take about eight weeks before Alvarez is ready to return to the field.

Alvarez injured his thumb Friday night in Los Angeles.

“We’re looking at eight weeks because of the position he plays and it’s the left thumb receiving as a catcher,” manager Carlos Mendoza said. “It’s one of those where we have to be mindful. I know he’s going to try to push it but we’ve got to make sure we get him back healthy.”

Over the past two years, four different players have had surgery to repair a torn UCL in their thumbs. Three of the four missed at least nine weeks of action; the fourth was Brett Baty, who missed the final six weeks of the 2022 season for the Mets and would likely have needed additional time to return.

Alvarez’s surgery included an internal brace in his thumb.

Alvarez should be able to resume baseball activities when he regains about 80 percent of his grip strength in the left thumb, Mendoza said.

Rebuilding the strength in that thumb is important, obviously, for what Alvarez can do swinging a bat. But it’s also critical to another of his most valuable skills: framing pitches at the bottom of the strike zone. Alvarez ranks among the major-league leaders in framing, and he’s at his best at the bottom part of the strike zone.