Two NFL sources tell ESPN 1500 Twin Cities Vikings C John Sullivan underwent microfracture surgery on his left knee last week.
According to beat writer Tom Pelissero, Sullivan's surgery was "relatively minor" compared to normal microfracture procedures, and there's "no doubts" he'll be ready for the regular season. Sullivan is tentatively expected to require 3-4 months of rehabilitation. Players are often never the same after microfracture surgery, while setbacks are common. It doesn't appear the concern level is very high with Sullivan, however. Entering season two of a six-year, $25.6 million contract, Sullivan was Pro Football Focus' top rated center in 2012, and a beast of a run blocker as Adrian Peterson came within yards of the single-season record.