The concern is he could be out indefinitely. Amendola is out this week versus the Washington Redskins, but that was the Rams' expectation anyway.
Amendola, the Rams' reception leader last season, hasn't played since dislocating his left elbow in the opener against the Philadelphia Eagles and didn't practice Friday.
Bell hurt his left hamstring and Gibson hurt his right hip. Tony Wragge replaced Bell.
The Rams remained winless, losing 17-10 to Washington.
Adam Schefter is ESPN's NFL Insider. Information from The Associated Press was used in this report.