Smith suffered the injury in the first quarter of Sunday's 17-13 victory over the New Orleans Saints.
Smith would not speculate on if he might be ready for next weekend's regular-season game at Atlanta, where the Panthers (11-4) can wrap up the NFC South title and a first-round playoff bye.
"I'm not looking past Christmas," Smith said.
Domenik Hixon, who replaced Smith, caught the game-winning touchdown pass with 23 seconds left Sunday against New Orleans.
Smith said he felt the knee pop when he attempted to jump for a high pass from Cam Newton on a third-down slant pattern. He laid on the field in obvious pain for several minutes before walking off under his own power.
After being checked on the sidelines, Smith was taken the locker room, where it was determined he had a left knee injury. He made one attempt to return, but was taken back to the locker room and was ruled out.
Smith, the team's all-time leading receiver, has 64 receptions this season -- the second-highest total on the team.
"My thoughts are to play as soon as possible," Smith said. "That has nothing to do with what's at stake."