Rush completed eight of nine passes for 92 yards and two touchdowns in Saturday's preseason game against the Colts.
For the second straight game, Rush badly outplayed presumed Cowboys No. 2 QB Kellen Moore, and it's becoming a distinct possibility that the undrafted rookie will win the backup spot behind Dak Prescott. Dallas trusts Moore's intelligence and familiarity with coordinator Scott Linehan's offense in that role, but if Rush continues to put up big numbers in the preseason and makes it too risky for the team to try and place him on the practice squad, they may have little choice but to keep him on the 53-man roster in Moore's place.