Mafah suffered a chest injury during Saturday's preseason game against Seattle and has been ruled out for the remainder of the contest, Todd Archer of ESPN.com reports.
Mafah was ruled out in the second half after compiling nine yards on four carries along with six yards on one reception during his time in the game. He's jockeying for position in Dallas' RB pecking order with Malik Davis and Jaydon Blue, so it will be blow to his chances of earning the No. 2 or No. 3 role if he has to miss time beyond this weekend. Dallas' second preseason contest will be next Saturday versus Arizona.