The injury appeared to occur at the end of a 43-yard catch-and-run that resulted in a fumble when Dunbar landed awkwardly after having his legs tripped up.
"Totally forgive him, totally forgive him," owner Jerry Jones said Saturday of the fumble. "I'm so glad our fans got to see him. He's quick, fast and makes plays. He certainly was the highlight for us tonight even though he had that fumble."
The Cowboys were counting on Dunbar as a change of pace to DeMarco Murray as well as a potential third-down back. Now that Dunbar's status for the start of the season is in doubt, Randle and Phillip Tanner will back up Murray.