There are 30 teams in the league that would like to have Jackson, a rusher who has put up seven straight 1,000 yard rushing seasons on mostly porous St. Louis Rams teams.
While Jackson is a fan favorite in St. Louis, he is 29 years old, well past the prime for any running back, and only in very special circumstances do running backs over 30 make a big impact for their team—but Jackson is one of those backs.
In comes the problem of the salary cap. Jackson, who makes $7 million this season, would only be available to a handful of teams. Consult the NFL's table for cap room concerning each team.
While New England is currently ranked fourth in the league in rushing, if they are serious about trying to repeat as AFC champions and getting back to the Super Bowl, they might want to pick up some insurance for young running back Stevan Ridley. He has been amazing this season, but has no experience.
The Green Bay Packers on the other hand, are ranked 22nd. While their old back, Ryan Grant, has been available for some time now after being released by the Washington Redskins, the Packers might not be interested in taking Grant back, making Jackson a prime option.
With the Pack getting over early struggles—such as the blown touchdown call against Seattle and the loss to Andrew Luck and the Colts—they have walloped their past three opponents, including a very good Houston Texans squad.
With Aaron Rodgers playing championship-caliber football, it makes sense for Green Bay to pick up the soon-to-be unrestricted free agent Jackson for what would be a reasonable asking price, in the form of a draft pick. The Packers are hoping that pick comes in at 32nd overall after the year is done.