The news on injuries along the Vikings offensive line has gone from bad to worse.
According to 1500 ESPN, the news likely means Sullivan's 2015 ended before it even began.
"He had a relapse about 10 days ago in the weight room so he had another procedure on his back," Zimmer said. "We don't know when he'll be back or if he'll be back (this season)."
Zimmer said the chances that Sullivan would return were probably minimal.
Sullivan first noticed the injury during preseason. Sullivan and the team tried to give it time to heal, until surgery was the best option. He underwent a lumbar microdiscectomy before the team's regular season opener at San Francisco.
Sullivan was placed on the injured reserve list – designated to return. Earlier this month, he told reporters he was encouraged with his progress, but wasn't sure on his exact return date.
"It's disappointing," Zimmer added Monday. "He was really doing really, really good (with his rehab) and this happened."
Zimmer added that backup center Joe Berger will continue as the starter as long as he's healthy.