The former West Germany international has paid tribute to Los Blancos boss Jose Mourinho for turning a collection of individuals into a "great team"
The Bavarians host Los Blancos in the first leg at the Allianz Arena on Tuesday night and the former West Germany forward is well aware of the enormity of the challenge facing his club, admitting that he believes the Liga leaders to be on the same level as reigning world, European and Spanish champions Barcelona.
"It will be incredibly difficult against Real Madrid," Rummenigge is quoted as saying by MARCA.
"We are awaiting one of the two best teams in the world, the leaders of the league in the strongest country in the European football.
"Jose Mourinho has turned a handful of individuals into a great team. They will be a tough nut to crack."
However, Rummenigge remains hopeful that Bayern will be able to spring a surprise and set up a 'home final' at the Allianz Arena against the winners of Barca's semifinal showdown with Chelsea.
"All of Spain is secretly dreaming of a Clasico in Munich," he argued. "But with two good games, we can make it so that Bayern takes part in this particular 'Clasico'."
Bayern's clash with Madrid is scheduled to kick off at 2:45 p.m. ET.