Jordy Nelson underwent knee surgery Monday and he will be out for the rest of training camp.
The Packers are "hopeful" that Nelson will be back for Week 1. Considering that's just four weeks away, the surgery was likely some kind of scope or MCL repair. Nelson did miss four games last year and was limited in a handful of others, but that was due to hamstring and ankle issues. He hasn't had a knee problem since 2009. Regardless, Nelson now appears highly unlikely to hit the ground running even if he does suit up against the Niners on Sept. 8.

Source: Rob Demovsky on Twitter