Newton had ankle surgery in March and was limited in offseason workouts before being cleared on July 24.
"It's all based on what [head trainer Ryan Vermillion] and the doctors think and how Cam feels," said Rivera. "Once we get past ... Thursday morning, we'll find out how he is after the practice and we'll sit down and talk and make a decision on what we want to do, in as far as he's concerned, in terms of playing time."
On Thursday, Newton said he's making daily strides but "still kind of reluctant with mobility," according to Alex Marvez of FOX Sports 1.
Rivera said that if Newton does play Friday against the Buffalo Bills, it won't be for more than a series or two and would mostly involve just handing the ball off.
Carolina opens the regular season on Sept. 7 at the Tampa Bay Buccaneers.
- Molly Geary