Report: Matt Forte's knees a concern

One key reason the Chicago Bears are yet to offer a long-term deal to running back Matt Forte is that the team is concerned about whether his knees will hold up, the Chicago Tribune reported Saturday, citing a source.

The source said the Bears want to protect themselves from arthritis setting in and becoming a chronic problem for the 26-year-old.

Forte, however, had a message for the Bears on Saturday, tweeting a video of himself running uphill with a weighted sled.

"100Lbs sled up hill i think my knee will be ok," he wrote.

Forte's knees have reportedly been a concern for some time, with the Bears among several teams that paid particular attention to the issue prior to his selection in the 2008 NFL Draft.

His previous injuries include a torn posterior cruciate ligament in his left knee in 2006, a sprained MCL in the same knee in 2009 and a sprained MCL in his right knee in 2011 that forced him to miss the last four games of last season.

Forte, who had 997 yards in 12 games last season, is yet to sign a one-year franchise tender guaranteeing him $7.7 million.

He skipped the first week of organized team activities because of the contract dispute.