The Boston Celtics beat the San Antonio Spurs on Saturday to win their second straight game, but the victory may have come at a cost. Marcus Smart sustained an injury in the game and wasn't able to return.

Smart suffered a knee contusion early in the third quarter of the contest after hitting Zach Collins off a hard screen. The Celtics guard fell hard to the floor and seemingly tried to nurse his left knee before he was taken off the floor, limping and clearly in pain.

Smart was initially labeled as doubtful to return, though he never returned as the Celtics survived the Spurs, 121-116. The reigning Defensive Player of the Year played in just 21 minutes before his exit, tallying five points, two rebounds, four assists and one steal.

The severity of Marcus Smart's injury has yet to be revealed, though the Celtics are certainly hoping that it's not serious and won't be a long-term issue. After all, he is the team's defensive anchor and his absence will certainly be a huge blow to them.

Boston is only starting to get their defensive identity back with Smart and Robert Williams III leading the way. But if Smart gets sidelined for some time, it could very well hinder the strides they have made on that end.

Smart is averaging 11.2 points, 3.4 rebounds, 7.3 assists and 1.3 steals per game. While those are not eye-popping numbers, every Beantown faithful knows that Smart brings plenty of things that aren't seen on the scoresheet.