The Miami Dolphins fear quarterback Ryan Tannehill suffered a torn ACL in the 26-23 win over the Arizona Cardinals on Sunday.
Tannehill limped off the field late in the third quarter after being hit around the legs by defensive lineman Calais Campbell on a pass completion.
Tannehill had already thrown three touchdown passes to that point.
Dolphins coach Adam Gase told reporters after the game the team is concerned Tannehill suffered a torn ACL.
Back-up Matt Moore came into the game and preserved the victory after the Cardinals mounted a comeback.
The Dolphins are now 8-5 and appear on track to make the playoffs for the first time since the 2008 season, but it appears Moore will have to fill Tannehill's shoes the rest of the way.