NEW YORK — Mets catcher Francisco Alvarez doesn’t have time to sit around and feel frustrated.

Nine days after tearing a ligament in his right thumb while sliding into second base, Alvarez is ready to go on a rehab assignment.

Before the Mets’ 6-5 win over the Philadelphia Phillies on Tuesday, Alvarez reported that he doesn’t “feel any pain” in his thumb.

“It’s surprising,” Alvarez added. “I thought, initially, when I got injured, that there would be more pain or a level of discomfort. But up until now, there’s none of that.”

The speed of Alvarez’s recovery surprised even Mets manager Carlos Mendoza. On Sunday, while the club was in Atlanta, Alvarez was back at Citi Field taking batting practice.

“I was like, ‘No way this guy’s swinging that bat,’” Mendoza remembers thinking after getting off the phone with staff.

Alvarez continued taking batting practice on Monday and Tuesday with the same rigor and force he had before the injury. He also reported to feeling no pain while throwing the ball.

“I’ve been throwing the same number of days that I’ve been hitting,” Alvarez told reporters. “In the beginning, it was a little bit strange just because I’m putting pressure on the fingers on top and not necessarily with my thumb.”

Alvarez missed almost two months last season with a similar thumb injury on his left hand. He returned just in time to help the Mets make their memorable postseason run.

After struggling at the start of this season, Alvarez was sent down for a month-long stint in the minors. He was quickly a force in the lineup after getting called back up at the end of July.

He’s 20-for-63 (.323 batting average) with 13 extra-base hits, including four home runs and 13 RBIs, in 21 games since then.

“I believe that I’ll be capable of returning as the same player,” Alvarez said. “If there is an instance where there is pain or discomfort, I will tell the coaches and staff about it, and I won’t play.”