The Uruguayan scored from the spot to give PSG a 1-0 lead at home to Bordeaux three minutes before half-time in their Ligue 1 game.
However, replays showed him grimacing in pain after the goal, and he then came across towards the touchline to talk to coach Thomas Tuchel before heading to the dugout as the final seconds of the first half were played out.
Cavani was then replaced by Kylian Mbappe at the start of the second half.
An injury to Cavani, who is PSG’s all-time leading scorer and has netted 22 times this season in all competitions, would be another huge blow to the French champions ahead of the Champions League knockout stage.
They are already missing Neymar for the last-16 tie against United, with the Brazilian not expected back from a metatarsal injury until early April.
He was in attendance at Saturday’s game, which saw Marco Verratti make his return to action after three weeks out with an ankle injury.