EDEN PRAIRIE, Minn. (AP) — Minnesota Vikings center John Sullivan has undergone a second surgery on his back, putting his return to the field this season in doubt.

Coach Mike Zimmer said Monday that Sullivan aggravated his injury while weightlifting about 10 days ago. He said the likelihood of getting Sullivan back this season was "minimal."

Sullivan was placed on injured reserve Sept. 10 with a designation to return, so the Vikings were expecting him to be healed by midseason. Joe Berger has taken Sullivan's place in the starting lineup.

Defensive tackle Sharrif Floyd was wearing a walking boot Monday on his injured left foot, leaving his availability in question after missing the game Sunday at Detroit. Zimmer said Floyd has some cartilage damage.