The Italian league will restart following the current international break, and both sides will clash next Sunday.
The Rossoneri have suffered a string of poor results this season under the management of Leonardo, who has been installed as head coach in the summer.
Ranieri hopes that Milan 'haven't been buoyed by the break'.
"Milan have Clarence Seedorf, Andrea Pirlo and so many other players of great quality," Ranieri told Roma Channel.
"It is a squad of champions and I hope they haven’t been buoyed by the break. The time together to train might well have given them the opportunity to fix some of their problems.
"In any case, we have to focus on improving ourselves and battling for the victory at all times.
"Then any result is acceptable, but the mentality has to be to go for the maximum, anytime and anywhere."