Jackson stepped on the cleat of a Patriots defender in a half-speed drill, hobbled off the field and did not return. Coach Jay Gruden said Jackson twisted his ankle "just a hair."
Jackson previously sat out one practice because of a sore hamstring. However, Gruden said Jackson still could play Thursday.
The same cannot be said for fellow receiver Pierre Garcon (hamstring), who will not play against the Patriots. Safeties Ryan Clark (hamstring) and Phillip Thomas (hamstring) will also sit out Thursday's game.
Gruden reiterated that defensive end Jason Hatcher remains close to returning. Gruden said he is eyeing the third preseason game for Hatcher.
Jackson is a centerpiece of the Redskins' passing game, and Thursday would be the first opportunity for him to work in a game with quarterback Robert Griffin III.
Gruden said it's likely, though, that the starters will play only eight to 10 snaps against the Patriots.
Griffin talked about needing to see how Jackson runs in game speed, just to get their timing down. But they've had a lot of work together in practice. Still, if Jackson can play, the Redskins would like to get him on the field.
"We'll see how he does at rehab or treatment," Gruden said. "It was a fluke [injury]."