Backup Derek Anderson started against the Titans, and he was expected to be followed by Joe Webb and Garrett Gilbert.
Newton threw a handful of passes to receivers in one-on-one and seven-on-seven drills on Thursday, but the 2015 NFL MVP's timing appeared to be off and several fell incomplete, according to the Charlotte Observer.
"You could tell he was rusty,'' Panthers coach Ron Rivera told reporters Thursday. "A couple late (balls) on the decisions he made. When he was throwing the ball, he was throwing the ball well, so we're not concerned about that.
"Now it's just a matter of him working himself back into shape where he can go out and take normal reps instead of us having to make sure we monitor him.''
Newton was held to a "pitch count" leading up to the preseason game in Nashville, Tenn., after 12 days of not throwing in team warmups or drills during training camp.
The 28-year-old star quarterback, who also did not play in last week's preseason opener against the Houston Texans, continues to rehabilitate his surgically repaired throwing shoulder. He had surgery on March 30 to repair a partially torn rotator cuff that was expected to require a four-month rehab process.
Rivera has not been concerned if Newton ends up missing all four preseason games, with the goal being to have him ready for the Sept. 10 opener on the road against the San Francisco 49ers.
Newton's injury occurred in the Panthers' Week 14 game against the Chargers last season. He played in each of the team's remaining three games and underwent offseason MRI exams to monitor his progress before deciding on surgery.
Newton passed for 3,509 yards with 19 touchdowns and 14 interceptions in 15 games last season for the Panthers, who missed the playoffs after finishing last in the NFC South with a 6-10 record.