Njoku, who was injured in the first quarter of Monday's game and also suffered a concussion, could require surgery for the wrist, a source told ESPN's Adam Schefter.
Both of Cleveland's starting cornerbacks, Denzel Ward and Greedy Williams, are questionable after suffering hamstring injuries this week. Safety Morgan Burnett (quad) also didn't practice Friday and is listed as questionable. The Browns have already ruled out safety Damarious Randall for Sunday due to a concussion.
In response, the Browns signed cornerback Robert Jackson to the active roster off their practice squad and claimed safety Juston Burris via waivers from the Raiders.
"The guys that are there [against the Rams], I expect us to show up and play well, compete every snap," Browns coach Freddie Kitchens said. "The expectations haven't changed. I just need 11 on each side of the ball to show up and play."
The Browns were already without linebacker Christian Kirksey (chest), who was placed on IR Saturday. Kitchens said Friday that Kirksey is getting opinions on whether he will need surgery.