Manziel left with 1:49 remaining in the first half with a hamstring injury aggravated on a 1-yard loss when tackled on the sideline by Carolina linebacker Luke Kuechly and defensive back Colin Jones. He did not return.
While he was on the ground being attended to by the training staff, some of the fans at Bank of America Stadium cheered.
"The only thing I can say is it was sad to see the crowd's response when he was getting hurt, man,'' said Newton, who led Carolina to a 17-13 victory 12 days after fracturing two small bones in his lower back in an automobile accident.
"I just think it was classless at that time. Anytime a person is hurt, you don't celebrate. I've had that done in my career. It takes the integrity out of the game.''
Fans in the Louisiana Superdome cheered during a Dec. 7 game when Newton appeared hurt after a 2-yard run off the left side in a 41-10 victory over the New Orleans Saints.
Newton didn't make a big deal about it then, but Carolina linebacker Thomas Davis did.
"There's really no place for that," Davis said at the time. "That's something that as a player, you never want to see a guy get hurt. When the fans are cheering because they think a guy is hurt, that's disgraceful."
Manziel had completed only 3 of 8 pass attempts for 32 yards when his day ended. Newton, the 2010 Heisman Trophy winner, shared a few words with the 2012 Heisman winner after the game.
"I'm a fan of his just like a lot of people are,'' Newton said. "But [there's] a lot of things he has to learn. It's a learning curve ... I told him I was pulling for him. Hopefully, during the offseason we will link up.
"But for the crowd to respond in that type of way, we'e better than that. That's not who we are."