MILWAUKEE — The steal of the draft is now facing rehab.

In a big blow to his development, Knicks rookie forward Cleanthony Early underwent arthroscopic surgery Tuesday to remove a loose fragment from his right knee. He is expected to be out at least a month to six weeks.

The injury was diagnosed following an MRI exam earlier Tuesday, but coach Derek Fisher said the Bronx native had mentioned discomfort during training camp. Early, who went to high school at Pine Bush in Orange County, will be reevaluated in a month to determine the timetable for his return, the team announced.

“I don’ t think it’s been bothering him for a while — maybe in preseason he mentioned it kind of in passing,’’ Fisher said. “We feel bad for Cle, just because he’s a young guy who’s been doing everything we’ve asked him to do. He comes early to practice every morning and was working hard. I hate to see him go through this setback. He’ll bounce back fine. We’ll miss him, but he’ll be good.’’

The second-round pick out of Wichita State — the first draft selection of the Phil Jackson era — has appeared in seven games this season for a total of 54 minutes. The 34th overall pick, whom some experts considered a steal after falling out of the first round, started the season out of the rotation but has made spot appearances.

Early, 23, has averages of 2.7 points, 1.0 rebounds and 0.6 assists while connecting on 7-of-20 shots, including 4-of-10 from 3-point land.

He probably will play rehab games with the Knicks’ D-League squad in Westchester upon his return from injury next month.

Team orthopedist Answorth Allen performed the surgery in New York.

On the state of his team’s poor 3-point defense, Fisher reiterated it’s not the priority.

“What we’re trying to do is help our team understand it’s the paint, rim and free throws, second chance and transition points that ultimately beat you,’’ Fisher said, going against the recent analytics trend. “If a team does hit 3s, that’s not the one factor that determines wins or losses. I don’t want to send a message we want to stand around and watch people shoot threes. I think we have to protect our paint first and we can improve on our ability to close out with technique and effort.’’