"I think he's ready," Rivera told reporters Sunday. "You wish he'd had a few more snaps and played a little bit earlier in the preseason so we'd have more to go on. But what we saw, we liked. We liked how everything seems to be meshing together as an offense. We'll see how it goes as we continue to work this week."
Newton, 28, underwent offseason surgery on his throwing shoulder. He threw just two preseason passes but has been working with the first-team offense throughout training camp.
Rivera compared Newton's status to his rookie year last week. The top overall pick in 2011 missed all of OTAs and minicamp due to the lockout.
"I think he's still taking steps. You really won't know until the opener. That's just the way it is," Rivera said, per Joseph Person of the Charlotte Observer. "Nobody knew what he was going to be like his rookie year. That's kind of how this is going to be. You won't know until we open up in San Francisco."
Newton is coming off the worst season of his professional career. He compiled 3,509 yards and 19 touchdowns against 14 interceptions in 2016, adding a career-low 359 rushing yards. It was a precipitous decline from his 2015 MVP campaign.