The Robins boss took the gong for November following the club's recent upturn in form.
"We'll make sure we're ready for Derby," Millen told the club's official website. "If I can start out on the road to Manager of the Month for December with a win, that would be good.
"I know the kiss of death has happened a few times over the years and I'll be looking to avoid that.
"It's a shame the Nottingham Forest match was called off because we had hit a good run of form and felt confident going there.
"Derby will be another tough test."
Source: PA
Source: PA