Rivera didn't specify which of Allen's feet was injured.
Allen sustained the injury in the fourth quarter of Carolina's 31-24 win over Seattle on Sunday, but finished the game.
The 33-year-old Allen has 136 career sacks — tied for most among active players — but a career-low two sacks since being acquired in an early-season trade with Chicago.
Rivera says the team hasn't decided whether to put Allen on injured reserve. If they do, he says the Panthers could promote former starter Wes Horton from the practice squad.