Coach Mike Pettine provided the update after the Browns completed a joint practice with the Buffalo Bills on Tuesday.
Pettine says Pryor aggravated the injury in practice a day earlier. Pryor had just returned to practice on Saturday after missing more than a week.
Gilbert was hurt 40 minutes into practice when he tumbled to the turf while defending Bills receiver Tobias Palmer during a one-on-one drill. The 2014 first-round draft pick was slow to get up, and then limped to the sideline where trainers wrapped the upper portion of Gilbert's right leg.
Pettine didn't know if Gilbert could play Thursday, when Cleveland hosts Buffalo in a preseason game.
Pettine expects Pro Bowl cornerback Joe Haden to sit out one more game to rest his hamstring injury.
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