Minnesota Vikings center John Sullivan has not played a single game this 2015 National Football League (NFL) regular season, and such will likely continue after having his second back surgery for the year. 

ESPN reported that Sullivan had a back surgery before the 2015 season began, earning him a spot in the short-term injured reserve. 

But during Vikings head coach Mike Zimmer's conference earlier this week, he discussed what happened to the 30-year-old footballer which may sideline him for the remainder of the season. 

"He had a relapse about 10 days ago in the weight room and he had another procedure done on his back. We don't know when he'll back or if he'll be back [this year]," Zimmer said, according to the Star Tribune. 

Zimmer also called the recent setback "disappointing" since Sullivan was doing great recovering from his first back surgery until the unfortunate incident happened. 

The sixth-round pick by Minnesota in the 2008 NFL Draft had not missed a game in the past three seasons and had been a starter since his second season with the team. 

Sullivan was expected to boost the offensive line of the Vikings in his return but it looks like they will now have to rely on his replacement in veteran center Joe Berger. 

Berger, who was selected 207th overall in the 2005 draft, has started in place of Sullivan in all six of the Vikings games this season. 

The 33-year-old has been a backup in his entire NFL career but will have to step up, now that there is a strong possibility he will be starting for the rest of the season. 

Zimmer is confident in Berger taking over the starting duties at the center position and expressed it during the conference. 

"I thought he's done a good job. He's getting guys for the most part in the right place. We've had a few mishaps here and there when we've had the wrong assignments. But overall he's done a good job," Zimmer said about Berger. 

The Vikings will be in action this Sunday taking on the Chicago Bears for their Week 8 game.