Gaffney signed to the 49ers' practice squad Tuesday, Can Inman of The San Jose Mercury reports.
Raheem Mostert (ankle) has already been ruled out for Saturday's matchup with the Cardinals. Jeff Wilson (ankle) is also questionable, leaving Tevin Coleman and Jerick McKinnon as the only two healthy backs on the roster. If the 49ers are looking to add extra depth on gameday, Gaffney's number could be called.