Kelly Gregg will have microfracture surgery on his left knee today, ending the season for the Ravens nose tackle, his agent said last night.
A starter since the 2002 season, Gregg likely won't be cleared to return until offseason workouts in May or June, agent Jack Bechta said.
"It wasn't responding to anything," said Bechta, who first reported the story on the Web site nationalfootballpost.com. "He knew it was time to move on."
A phone call to a Ravens spokesman was not returned last night.
Gregg, 31, injured his knee in the first week of training camp. He had arthroscopic surgery in August to smooth out a groove on the bone of the knee.
The Ravens were optimistic that he would be ready for the regular season, but Gregg began having a cartilage issue with the knee.
He missed the entire preseason as well as the first four games of the regular season. His surgery will be performed by Dr. James Andrews.
"We got to the point where it was not feeling better," Bechta said.
Gregg, who had missed just three games in his previous six seasons, has the most tackles for any interior lineman (398) in the NFL since 2002.
Justin Bannan, who has replaced Gregg, is expected to remain the starter for the rest of the season.