Real make the trip to the Etihad Stadium knowing victory will book their place in the knockout stages and dump out City.
Real are currently second in Group D a point behind leaders Borussia Dortmund.
Callejon admits the clash with City is a must-win encounter for Jose Mourinho's men if they want to top the group and he insists they will attack against the English champions.
"Now we are off to Manchester and we have to take all three points so that we can top the group," Callejon told AS. "Winning a game like this before is the perfect send-off for us."