The Celtics guard was ruled out in the third quarter of the 113-104 win after taking a "direct blow to the abdomen" in attempting to take a charge against Knicks forward Kevin Knox.
"The only thing I heard is that it was, I don't know if it's his oblique, or right in that area, and they said, 'It wasn't as bad as in the past,'" Celtics coach Brad Stevens said. "I don't know what that means. I'm sure we'll get more information in the next couple hours."
Smart, who was called for a blocking foul on the play, immediately began writhing in pain, and stayed down for a lengthy period of time. Eventually a timeout was called, and Smart was helped up off the ground. He then needed assistance to make his way back to Boston's locker room.
The "past" injury Stevens was referring to was when Smart ran into the hip of Orlando Magic center Nikola Vucevic back in April, causing him to miss about a month with a left oblique tear. It was a similarly benign play, and was followed by a similar reaction from Smart, down to grabbing at his left side and being in severe pain. Smart confirmed to NBC Sports Boston on his way out of the arena that he was hit in the "same spot" as he was back in April.
The Celtics are also expected to get an injury update Monday on the status of forward Gordon Hayward, who has been out for the past three weeks since undergoing surgery on a fractured bone in his left hand on Nov. 11. Hayward, who participated in non-contact, 5-on-0 portions of Saturday's practice and was shooting before the game Sunday while Celtics owner Wyc Grousbeck looked on, is scheduled to have a FaceTime consultation with his doctor Monday to determine whether he can return to contact practice.
Boston said Hayward was expected to return in approximately six weeks when his surgery was announced.