Stewart was placed on the physically unable to perform list Tuesday after meeting with team doctors about his injured right ankle. He will miss the first six weeks, which means DeAngelo Williams will open as the top back with the combination of Armond Smith, Tauren Poole and possibly Kenjon Barner behind him.
Fullback Mike Tolbert (hamstring) also will figure into the mix if he returns as expected by the opener. Because the Panthers have a bye in Week 4, Stewart could only miss five games. Stewart and coach Ron Rivera remain hopeful the team's second all-time leading rusher will return this year.
"I can spend all my energy being disappointed, or I can spend all my energy preparing myself for Week ,'' Stewart said as he left the practice field.
". . . As of right now just taking it day by day. Just be there for my teammates and bring as much positive energy as I can. . . . We've got a long season ahead of us, and I plan to be back Week .''
Stewart wouldn't go into detail on what is going on with his ankle.
"It's kind of hard to explain, but it's painful,'' he said.
Stewart signed a five-year, $36.5 million contract extension last season, but struggled with injuries to both ankles and finished with 333 yards and one touchdown. He underwent offseason surgery to repair the damage, but his right ankle has continued to give him problems.
When healthy, Stewart gives the Panthers two solid options at running back with Williams.
Stewart averaged 5.4 yards per carry in 2011, when he rushed for 761 yards with only three starts, and 5.1 yards per carry for 1,133 yards in 2009 with three starts. His career average is 4.7 yards per carry. His 3,836 yards rank second in team history. Carolina's running game has struggled during the preseason with Williams and Barner carrying the bulk of the load. The team has 166 yards on 57 carries for a 2.9 average.
But Rivera is confident in the backs he has and doesn't plan to bring in another player.
"I'm very optimistic,'' Rivera said. "The doctors just feel right now with the way it is, it's going to take a little longer [for Stewart]. We feel good about DeAngelo and the young running backs we have in place, and we'll go forward with those guys.''
The Panthers got more bad news in that fourth-round draft pick Edmund Kugbila, expected to contend for a starting job on the offensive line at guard, was placed on injured reserve with a knee injury.
Rivera said Kugbila had "flashed so hard for us'' during the preseason and he was excited about his potential.
"The long-term with our medical staff they just really feel this is the best thing for him,'' Rivera said. "It's a long-term of getting him ready to go and looking towards the future with him.
"Disappointed. We're going to miss a good young football player who could help us like the other four guys are getting ready to help us.'' Carolina waived injured defensive tackle Frank Kearse and wide receiver Joe Adams. If they clear waivers over the next 24 hours they could return to the practice squad.
Those moves along with putting Stewart on PUP put the roster at 75 players.