Watkins was having a big game, with six catches for 106 yards and two touchdowns, when he left with about eight minutes remaining in the fourth quarter.
He appeared to take a hard hit as he barreled into the end zone for his second score, on a 13-yard reception that gave the Rams a 41-26 lead.
Watkins was evaluated in the medical tent on the Rams' sideline before heading to the locker room, and he was placed in the concussion protocol, according to McVay.
Austin left the game shortly after and also was placed in the concussion protocol, McVay said. Austin finished without a reception but had three carries for 14 yards.
The Rams (2-1) have 10 days before their next game Oct. 1 at the Dallas Cowboys.