Warne, 36, spent several years with the Millers gaining promotion to the Championship along the way, and was released by Yeovil last month.
"I know Paul Warne is fit, he did most of my running outside of the penalty area," said Millers boss Mark Robins jokingly to Radio Sheffield.
The Millers are still seeking to strengthen attacking wise and have also brought in one of the two potential players that were on offer from Stoke City in Marc Grocott.
"Marc Grocott has got good movement and can finish, but he may be one we take on and develop for the future." added Robbo.