"He's still taking steps," Rivera said following practice Tuesday. "You really won't know 'til the opener. Just the way it is. Nobody knew what he would be like his rookie year. That's kind of how this is going to be. We won't know until we open up in San Francisco."
Rivera remained noncommittal on whether Newton, who had surgery on March 30, would play in the preseason finale Thursday against the Pittsburgh Steelers, and said he would be all right if Newton's only preseason snap was the one-play, 75-yard touchdown drive he had on the first series Thursday of a win at Jacksonville.
"You do what you have to do,'' Rivera said. "He's on track. He's done some good things. But every day you wake up every morning wanting to make sure he's fine. He's done everything we've expected so far, so going forward we'll see.''
The last time Newton played in the preseason finale was his rookie season of 2011. He played one series, completing three of five pass attempts for 25 yards on a nine-play, 71-yard touchdown drive. He also rushed one time for 19 yards.
If Newton, who in 2015 signed a five-year, $103.8 million extension, plays against the Steelers the Panthers likely would have to play their starting offensive line and wide receivers.
That would put not only Newton, but also left tackle Matt Kalil, center Ryan Kalil, Pro Bowl tight end Greg Olsen and wide receiver Kelvin Benjamin at risk of injury. Kalil is coming off hip surgery and Ryan off shoulder surgery.
Rivera hasn't been willing to risk key starters in the finale the past six preseasons. None played last year against Pittsburgh.