Two weeks after undergoing knee surgery Green Bay Packers wide receiver Jordy Nelson is unsure whether he'll be ready for the start of the regular season.

When coach Mike McCarthy initially announced Nelson's surgery he expressed hope that the 28-year-old's absence would only extend through the preseason. Though Nelson claims his rehabilitation is "progressing right on schedule" he also said that he's "slowly progressing."

With the Packers 20 days away from playing in San Francisco for their regular-season opener Nelson has some doubt that he'll be on the field with his teammates for that game.

"You never know" Nelson said Monday in the locker room.

Nelson wouldn't specify other than to describe his injury as a "knee issue" that flared up in a practice a few weeks ago. When asked of a report that suggested Nelson has been battling through this injury since his college career at Kansas State six years ago Nelson said "that's a little over the top" and added that it had gone away during his first five seasons in Green Bay.

"You want to avoid surgery as much as possible and that's what we tried to do" Nelson said. "I thought we had it taken care of and then we realized we didn't.

"I wasn't going to be able to be 100 percent. It was something I would have been able to play through if it would have happened in-season or something but there was enough time that we kind of took the chance that if everything went smooth we could get in and out during training camp and hopefully have a healthy 16-game season."

As Nelson noted he did take a chance by opting for the surgery. That chance was a calculation in terms of whether there was enough time -- 34 days to be exact -- for him to get game-ready by early September.

Nelson has been running during his work with the Packers' training staff. However much of that running has been done on a weightless machine that Nelson said "allows you to run and not put all the pounding on your legs."