IRVING, Texas -- Sean Lee's season is over.

The Dallas Cowboys announced they are placing the inside linebacker on season-ending injured reserve with a toe injury and will sign veteran linebacker Ernie Sims to fill his roster spot.

Lee will have surgery on his right big toe, according to sources, with a full recovery expected for 2013. The Cowboys feared Lee would need surgery but had held out a slim hope of a comeback but by late Tuesday, those hopes were extinguished.

Lee's agent, Michael McCartney, said Wednesday morning that Lee would be seeking a second medical opinion, but that the linebacker suffered a "significant tear."

"We're not hopeful," McCartney added. "I'm sure he's having surgery sooner rather than later."

Sims, 27, played in 13 games last year for Indianapolis with four starts and was credited with 32 tackles. In 2010 he started 15 games for Philadelphia and had 55 tackles and two sacks. He spent his first four seasons with Detroit.

Running back Felix Jones had a similar surgery in 2008 and has not had any issues with the toe since.

Lee suffered the injury in the third quarter of Sunday's win at Carolina. A second MRI on Tuesday confirmed significant ligament damage. He has the most severe case of turf toe with a complete tear.

Some players in the past have been able to play with milder cases of turf toe.

The Cowboys view Lee as a long-time piece to the future of the team, but he has had trouble staying healthy. He almost had his 2011 season come to an end with a dislocated left wrist but managed to miss only one game and played the rest of the season with a cast. He missed two games in 2010 with a hamstring injury after coming in with a knee injury.

Lee leads the Cowboys in tackles with 77 in the first six games, according to the coaches' film. He has two tackles for loss, eight quarterback pressures, one interception, two pass deflections and a forced fumble.

Dan Connor will replace Lee in the starting lineup, and Bruce Carter will take over as the defensive signal caller.

Calvin Watkins of ESPNDallas.com contributed to this report.