"I did not let him go today, but he's more than ready," Arians said, via the team's official website. "And Ryan (Williams) is full speed, so we're fully healthy at running back."
As long as Mendenhall is healthy, he is the clear lead dog.
We don't want to undersell that caveat, however. It's never a good sign when the team's top two backs miss multiple preseason weeks with knee injuries. As is the case with the offensive line, experienced depth is a concern in Arizona's backfield.