Jones suffered an Achilles injury that will require surgery, Cameron DaSilva of USA Today reports.
Initially, the undrafted rookie was believed to be dealing with a left ankle issue in the wake of his late exit from the Rams' exhibition finale Saturday. The Rams opted to waive him with an injury designation Tuesday, and he reverted to injured reserve on Wednesday. Considering the nature of the injury, it's a good bet Jones won't play this season, which would mean the Rams are down three running backs heading into Week 1. Currently, Darrell Henderson (thumb), Sony Michel and Jake Funk are the only RBs on Los Angeles' active roster.