ATLANTA — The Knicks could be without Josh Hart for their closeout Game 6 against the Hawks on Thursday.

The Knicks downgraded Hart to questionable with a lower back contusion after Game 5 at Madison Square Garden on Wednesday.

Hart left the Knicks’ 126-97 victory over the Hawks with roughly five minutes left in the fourth quarter and went directly to the locker room. He did not return to the bench, and head coach Mike Brown did not have an update on his starting forward immediately postgame. The Knicks downgraded him to questionable on Wednesday.

Hart sustained lower back spasms in the preseason opener in October and missed three weeks of action.

The starting Knicks forward is averaging 9.4 points, 10 rebounds, 4.8 assists and 1.6 steals through the first five games of the first-round series against the Hawks.

If ruled out, head coach Mike Brown could turn to backup guard Miles McBride, reserve sharpshooter Landry Shamet or defensive anchor Mitchell Robinson in the starting five.

Hart has been one of the Knicks’ two best defenders in this playoff series, helping hold Hawks All-Star Jalen Johnson to modest averages of 19 points in his first career playoff series. Hart has also played good defense on C.J. McCollum, who scored 26 and 32 points in Games 2 and 3, to just six points on 3-of-10 shooting from the field in Game 6.

Hart averaged 12 points, 7.4 rebounds and 4.8 assists during the regular season. He shot 41.3% from 3-point range during the regular season but had converted on just 16% of his 3s in the playoffs and shot 37% from the field through the first five games of the Hawks series.

Hart had nine points, five rebounds and four assists in the Knicks’ Game 5 victory at The Garden on Tuesday. He averaged 11.6 points, 8.8 rebounds and 4.8 assists on 37% 3-point shooting during the Knicks’ Eastern Conference Finals run last season, a run ultimately resulting in Hart being benched for Robinson against the Indiana Pacers.