DeGrom, who is 7-8 with a 3.04 ERA this season, hasn't pitched since Sept. 1, when he suffered a third loss in as many starts. Hehas been sidelined with forearm inflammation.
Manager Terry Collins decided deGrom would start Sunday after watching him throw a bullpen session that went approximately 30 pitches.
"I just saw him throw his pen," Collins said. "[He] threw the ball great."
Collins decided that Rafael Montero would not pitch Sunday after he was ineffective again in an 8-1 loss to the Nationals on Monday. Noah Syndergaard, who went seven innings in Tuesday's win over Washington,also was a candidate to start Sunday, but Collins said he wanted Syndergaard to have an extra day of rest before his next start.
"We talked to Noah, [and] he actually thought he could use an extra day after [Tuesday]," Collins said. "So we thought it'd be a good time to get Jake in there. Not only do we think he's ready ... we know how good he can be in the daytime.
"We'll probably limit the workload a little bit -- 75. If he gets the last hitter at 78 or so, [we'll] probably let him finish it. But he'll be right in that area."
Collins said the team is not expecting a vintage performance from deGrom on Sunday.
"Our expectations right now are to kind of build him back up a little bit," Collins said. "I think he will dictate a lot by how he feels, but we certainly hope -- he's basically going to get three starts -- we're hoping that we can get him back up to where, if we get in the postseason, he's a viable option for us. We certainly think he's going to be fine, but we don't have a crystal ball here to know what's going to happen after he throws Sunday.
"Obviously, the effort level's going to be pretty intense with him, and we'll see how he bounces back from it, but we're just glad to have him back."
Another Mets starter who has been sidelined, Steven Matz, is making progress toward a possible late-season return. Matz last pitched Aug. 14 and has been sidelined with a shoulder impingement. He is scheduled to throw a full bullpen session Saturday at the team complex in Port St. Lucie, Florida.
"If Steven can come back, that'd be a nice piece to have as we get into those last few games," Collins said.
Other injured Mets are back and ready to contribute, or at least close to returning. Former Gold Glove centerfielder Juan Lagares, who had surgery in July to repair a ligament in his thumb, is available as a defensive replacement or pinch runner. First baseman Lucas Duda, out since May with a stress fracture in his lower back, will rejoin the team Saturday, though it's uncertain how much he'll be able to contribute, because he hasn't faced in-game pitching in nearly four months.
Infielder Wilmer Flores had a cortisone injection to address inflammation in his right wrist and is still a few days from returning.