Butler left with 2:20 left in the first quarter after going scoreless but contributing four rebounds and two assists in 10 minutes.
Coach Brett Brown said after the game that he had yet to meet with his medical staff for an update on Butler’s injury.
“I don’t know the detail of it,” Brown said, “nor do I know what’s going to happen in relation to the longevity, how long he’s going to sit out.”
Butler has averaged 21.4 points per game since coming over to the Sixers in a trade with the Timberwolves last month.
Philadelphia has gone 10-3 since Butler joined the lineup.
Sixers star Joel Embiid, who recently expressed concern that his own offensive game has been subpar since Butler arrived, led Philadelphia with 24 points Monday.
Embiid sat out Friday’s game in Detroit after scoring 16, 15 and 10 in his previous three games.