It might seem like heresy to even consider the Packers letting Grant go, but the truth is about two weeks before the season opener the only certainties at the position for the 53-man roster are James Starks, Alex Green and John Kuhn.
When I first saw Green and Bold's Fanpost, I thought it was pure speculation. But then Kevin Seifert noted it too. And I will give Tom Silverstein at the Journal-Sentinel credit for having a lot more insight and access with the Packers than I have. So let's just walk this through.
The Packers have usually kept three running backs under Mike McCarthy. Injuries kept James Starks and Grant out most of last season, and Kuhn effectively became the third running back. After Starks returned, he was usually left inactive if Nance was active (or visa versa), leaving Brandon Jackson, Kuhn, Nance/Starks active each week.
With only two full backs (Kuhn and Quinn Johnson) likely to make the roster, I doubt the Packers would only go with four total backs on the active roster. They'll want to have three running backs. Starks and Green appear to be locks for two of those spots.
With Nance ahead of undrafted rookie Brandon Saine, that would leave Nance and Grant as the options. The Packers would save money by releasing Grant in favor of Nance, but I've never seen anything from Nance to believe he's actually better than Grant. Though he might be the best running back in pass protection.
While Mike McCarthy has spoken well of Green as a pass protector, he did miss on one block against the Cardinals, so he might not be ready for a role as a third down back. But he looked really good as a runner, showing nice patience for his blockers before making a quick move into an opening. He also showed his strength as he can't be taken down by an arm tackle. While I've been considering Green as a possible replacement for Jackson, maybe he's a replacement for Grant.
The coaches and front office have thought highly of Grant for years, and they wouldn't be quick to release him. McCarthy said that he "would like to start off getting Ryan going this week" so he seems to be interested in getting him ready for the regular season. While Grant would save them money, they are about $13 million under the salary cap and aren't being forced to trim payroll. In the carries I've seen from Grant this preseason, he looks like the same player except he's made a couple of poor choices in the open field that could be dismissed as rust from the long layoff.
My best guess at the moment is that Grant will remain as the starter, Starks will frequently replace him, and Green will be the third down back. But I could see Starks and Green emerge as the top two backs, and Nance becomes the third down back. If Green can do what Grant can do, plus Nance is a better third down back than Green, then the Packers might have a tough choice. If you're looking to see if Grant can keep his roster spot over the next two preseason games, don't compare him to Nance, but watch and decide whether Green can replace Grant.