Josh Hart has finally made his return.

The Knicks forward, who’s been sidelined since the preseason opener with a lower back injury, was upgraded to a game-time decision ahead of Friday’s matchup with the Boston Celtics after participating in full-contact practice for the first time since early October. Thirty minutes ahead of tipoff, the Knicks gave the green light.

“You don’t really know how often you use your back until you hurt your back,” Hart said Friday. “Last week I was feeling good, kind of hitting all my checkmarks, and then I tried to go through doing live contact stuff and it was just not there. It’s not ready yet.

“It’s frustrating ’cause I wanna play. I wanna compete. But I gotta be smart with it.”

Hart sustained what the team called lumbar spasms in the Oct. 2 Abu D

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