Coach Chan Gailey says Smith twisted his foot, but didn't specify the nature of Williams' injury Monday. It was the Bills' first practice since a 35-32 overtime preseason win over Jacksonville on Saturday.
Both were hurt in the game, but did not miss playing time. Williams had a sack and three tackles. Smith had four carries for 19 yards and an incompletion.
It's unclear whether either will play Thursday in Buffalo's preseason finale against Detroit.
Receivers Roscoe Parrish (hamstring) and Donald Jones (head), and running back Johnny White (head) returned to practice. Parrish expects to be ready for the regular-season opener at Kansas City on Sept. 11.