According to Adam Schefter of ESPN, Johnson has "loose bodies" in his sprained knee and has doctors recommending that he undergo offseason surgery.
However, the final determination of whether to undergo surgery will be Johnson's, Schefter reports.
In other words, the surgery isn't so serious that it's "required," although it's something that could keep Johnson from dealing with similar knee pain and struggles in 2014.
Megatron was listed as "questionable" for Week 17's matchup against the Vikings after not practicing all week long. He wasn't spotted on the field for warmups, which means his season could end sooner than expected.
That's probably the smart move (Adrian Peterson is already out for Minnesota in the meaningless matchup) and it could potentially set up Johnson to focus on getting his knee right quickly.