Finally, Yoenis Cespedes is back after more than two months on the disabled list. It remains to be seen, however, how long he can stay healthy.

The Cuban slugger has spent more time on the disabled list the past two years than on the field. The Mets activated Cespedes, out since May 13 with hip flexor, heel and quadriceps injuries, hours before the Subway Series opener Friday.

“He felt like he was really ready,” manager Mickey Callaway said before the Mets played the Yankees at the Stadium to open the second installment of the Subway Series.

But before Cespedes — who wasn’t made available for comment before the game — had taken an at-bat, Callaway said to expect the dynamic 32-year-old outfielder to be a late scratch on occasion when the team sees signs of fatigue.

“One thing we have to do is be proactive in making sure we do everything we can to keep him on the field as much as possible,” Callaway said of Cespedes, who has appeared in 118 of a possible 256 games since signing a four-year, $110 million contract before last year. “He’s got a routine that he has to go through to get ready every night and we’re going to monitor that routine quite extensively.

“Percentages go up [of getting hurt] when your body’s not in a great spot. If he looks tired or run down a little bit, there might be a time where he’s a late scratch and it’ll be because we determined it would be more risky to send him out there like that.”

His return will give the Mets’ feeble lineup, already without third baseman Todd Frazier and outfielder Jay Bruce, a major boost. Before his injury, Cespedes had a slash line of .255/.316/.474 with a .790 OPS along with eight home runs and 28 RBIs in 37 games. He played in two rehab games earlier this week in the Gulf Coast League and went 2-for-8 with a home run.

Cespedes batted second Friday night as the designated hitter, though Callaway said he could see some time in the outfield in the series. During his rehab, Cespedes began taking ground balls at first base and even played a game there with the Gulf Coast League Mets this week. He will continue to get some work at first base before games and at some point he could see action there.

“He needs more reps, [he has to] feel more comfortable around the bag,” Callaway said. “We’re going to work him out and make that determination when we think it’s the right time.”

The Mets are still in the process of figuring out if moving to first base will alleviate the stress on his legs that has limited Cespedes so much the past two seasons. Having him move between first base and the outfield during pregame workouts could have an adverse effect on Cespedes, Callaway said. But there is also the belief that playing first base would lessen the risk of injury, because he would be in constant motion unlike the outfield and would limit the times he has to run full speed.

“We’re still trying to determine [the best thing for him], to make sure that’s the best spot for him,” Callaway said.