Grant had to be carted off the field during Tuesday's practice after suffering the injury.
"I really feel awful for Jakeem," Browns coach Kevin Stefanski said Tuesday before the results of the follow-up tests were known. "We've witnessed how hard the young man has worked since he got to our team. We all realize injuries are a part of our game but that doesn't make it any easier to accept especially for someone that works as hard and carries himself like Jakeem."
The Browns signed Grant to a three-year deal this offseason to be their kick and punt returner; Grant, however, was also having a standout training camp as a receiver out of the slot, as well.
Earlier this week, Browns special teams coordinator Mike Priefer said he thought Grant would "transform" Cleveland's return game.
With Grant out, the Browns will likely turn to Demetric Felton Jr. to return punts and kicks.