Coach Ron Rivera is optimistic Newton, who missed most of the offseason recovering from surgery on his left ankle, will be ready to play in the Sept. 7 opener at Tampa Bay.
"I do [expect him to be ready], but a lot of it is he had to get past the soreness, which we expect, and we'll see how he starts to progress," Rivera said after Sunday's practice.
Newton was in a great deal of pain when he arrived at the stadium on Sunday. He was sent him for an MRI and CAT scan. The MRI revealed the hairline fracture suffered when New England linebacker Jamie Collins stepped on the quarterback's back, catching him at a vulnerable spot on the flak jacket at the end of a 7-yard scramble. He sat out a play and returned to the game.
Newton arrived at practice walking slightly hunched over and stiff.
"Very frustrating," Rivera said of how the injury took place. "The unfortunate part is he had a chance to make a play on it. He chose to tuck it and run. One thing he's going to have to learn is either dump it or learn how to slide."
The Panthers have kept Newton from running for most of the preseason as part of his rehabilitation from the ankle surgery. Rivera said on Thursday the ankle, in his mind, appeared 100 percent.
Rivera also said while he discouraged Newton from running, he wouldn't mind see the quarterback take off just to show he mentally is over the injury.
Newton wasn't the only starter out on Sunday. Left tackle Byron Bell (illness), right guard Trai Turner (groin) and defensive ends Greg Hardy (shoulder) and Charles Johnson (hamstring) also did not practice.
Starting strong safety Roman Harper (turf toe), who missed the first three preseason games, practiced for the first time since the team returned from training camp in Spartanburg. Outside linebacker Chase Blackburn (back) also was back after missing Friday's game.
But most of the focus was on Newton. Rivera said after the game he planned to start the No. 1 overall pick of the 2011 draft against the Steelers even though he traditionally hasn't in the regular-season finale.
Rivera wanted Newton to get one more chance to work on his timing with a new group of receiver after losing his top four from last season.
Newton was 8-for-12 passing for 88 yards against New England, but he missed a few open opportunities. He also was sacked three times.
Derek Anderson, whose wife is expecting the couple's first child, will start against Pittsburgh and be the starter at Tampa if Newton doesn't recover in time.
Rivera said Newton's injury increases the likelihood that Carolina keeps a third quarterback, Joe Webb, on the final 53-man roster.
Fourth-string quarterback Matt Blanchard suffered a concussion against New England and is going through the NFL's protocol for head injuries. He is not expected to play on Thursday.
Newton is expected to rest most of this week and be re-evaluated over the weekend.
"There is a lot of concern," Rivera said. "We'll treat it day by day and evaluate it at the end of the week and see how he is. We expect him to get past the soreness in the next few days and do a lot more."
Cam Newton Has Fractured Rib
ESPN Panthers reporter David Newton breaks down what Cam Newton's rib injury means for the team.