James retreated to the locker room with 3:48 remaining in the second quarter after he collided with Boston’s Jayson Tatum and was fouled.
Tatum’s left shoulder hit James’ face and jaw.
James opened the game by scoring 24 points on 9-for-15 shooting with four rebounds and four assists in 16 minutes.
Cavs forward Jeff Green subbed in for James, who returned to the game with 1:57 remaining in the second quarter.
Despite the injury, James finished with a game-high 42 points as part of a triple-double, but his Cavs fell into a 2-0 hole in the series with a 107-94 loss on Tuesday.