Mathis tore the Achilles tendon in his left foot last September while he was serving a four-game suspension for violating the league's ban on performance-enhancing substances.
"I don't think at this point anyone knows for sure,” Irsay said on the Colts website. “Obviously, Robert is optimistic, and he's a fast healer. You just don't know, but I would say I don't see him being football ready for the beginning of training camp where he would be a full-go guy and that sort of thing. I think time will tell.”
The 34-year-old, six-time Pro Bowler last played during the 2013 season when he led the NFL with 19.5 sacks.
The Colts report for training camp on Aug. 1. Mathis said last month that he would be ready by the team's season opener on the road against the Buffalo Bills on Sept. 13.
"I'm back running. Training and rehab is full swing. I'm ahead of schedule and just trying to stay ahead of it,” Mathis said.
Irsay says it could be as late as November before Mathis sees the field.
“Obviously, Robert wants to be back as soon as he can be. We want him back as soon as he can be, but we also want to make sure when he comes back that he's 100% healthy and ready to go,” Irsay said. “But as far as the start of training camp, I don't see him being as a full-go guy right when we're starting up."
- Scooby Axson