Rivera said it would be "difficult" and "very unfair" to judge the first pick of the 2011 draft because of everything that has happened during the offseason and season.
Newton underwent ankle surgery in March that forced him to miss most of the offseason workouts with a new group of receivers. He suffered fractured ribs during the preseason that forced him to miss the season opener.
At one point during the season Newton was without his top three running backs -- DeAngelo Williams, Jonathan Stewart and Mike Tolbert -- because of injuries. The offensive line, which began the season inexperienced, has been decimated by injuries to the point there has been change on a weekly basis.
The defense also has struggled since defensive end Greg Hardy was placed on the commissioner's exempt list prior to the third game.
"You go back and look at some of the teams that have struggled in the past that had great years [before]," Rivera said on Monday when defending Newton's performance. "One that pops to mind right away was what happened at Atlanta last year.
"A couple of years ago they go to the NFC Championship Game and the next thing you know they're struggling because they had a lot of things happen."
Atlanta went from 13-3 in 2012 to 4-12 last season. With injuries on the offensive line and to starting wide receivers Julio Jones and Roddy White, quarterback Matt Ryan's passer rating dropped to 89.6 in 2013 after a career-best 99.1 in 2012.
Newton has gone from a career-best 88.8 rating in 2013 when the Panthers went 12-4 to a career-worst 78.9 rating this season. The two-time Pro Bowl selection has 13 touchdown passes and 11 interceptions a year after having 24 and 13, respectively.
Newton has one year left on his original contract after the Panthers exercised his fifth-year option during the spring. General manager Dave Gettleman said after last season that Newton proved he is a franchise quarterback.
Newton said prior to the season he wanted a long-term deal and Rivera said in October that Newton would get a long-term deal in "due time." There was talk of Newton drawing a six-year deal in the range of $20 million annually early in the season when Newton was playing well and the team was 3-2-1.
But with the Panthers (3-8-1) mired in a seven-game winless streak and Newton struggling during that time, the question of Newton's long-term value has become a topic among NFL analysts.
Newton has particularly struggled in the first half, throwing only three touchdowns against six interceptions. His record this season is 2-8-1; his four-year record is 27-31-1.
There has been no movement on a long-term deal and Gettleman hasn't commented on the status of Newton or any players since the preseason. Again, Rivera said it would be tough to judge Newton based on this season.
"Judge him. Judge the team. Judge the players on the team. Judge the coaches," he said. "There's going to be a lot of evaluations we have to go through, not just us as players and coaches but our scheme, what we're doing, what happened, what people did to us."