But Warrington, the Millers' number one shot-stopper, holds no grudges against Robins for leaving the Don Valley Stadium club.
"Mark's done a great job for us," Warrington told the Sheffield Star. "It's sad to see him go, but I wish him the best of luck in the future.
"For his first job, he really had done a fantastic job. I'd have liked him to stay, but these sort of chances don't come round very often, so I wasn't surprised he's taken the opportunity.
"I hope he is successful at Barnsley, I don't think anyone could have any qualms to what's he done for this club; he's been a great manager."