NEW YORK -- Knicks rookie Kevin Knox was forced to leave in the first quarter of Saturday's 103-101 loss to the Boston Celtics because of a sprained left ankle.

X-rays for Knox were negative, and head coach David Fizdale said he wasn't sure if Knox would need an MRI. It was unclear whether Knox would make the trip for the Knicks' game against Milwaukee on Monday.

"I had a real bad feeling in my gut when he went down," Fizdale said. "Where my angle was at I could see the thing basically hit the floor, roll to the floor. I knew right away when he stayed down that it was a [significant] one. I feel for the kid."

Knox, 19, was driving for a layup on a fast break when his ankle appeared to roll badly as he was fouled by Terry Rozier III. Knox stayed on the court briefly, appearing in pain. He didn't put any weight on his left leg after the injury and was helped off the floor by teammates.

Knox couldn't shoot the subsequent free throws and was, by rule, disqualified from the remainder of the game.

The No. 9 overall pick in the 2018 NBA draft, Knox has been coming off the bench for New York early in the season. He played well in the Knicks' loss to the Brooklyn Nets on Friday night, scoring 17 points on 7-for-14 shooting.

If Knox is sidelined for a significant amount of time, it would be a tough loss for New York. The Knicks (1-2) are already without All-Star forward Kristaps Porzingis, who is rehabbing from ACL surgery.