After beginning their European programme with a draw against Napoli and that infamous 2-0 loss at Bayern Munich in which Carlos Tevez allegedly refused to play, City need to beat the Spaniards to kickstart their campaign.
De Jong said: "They are two massive games (this week). The Champions League is the first one and it is obvious we have to win that game to proceed to the next stage.
"After that is the United game, which will be a massive game, number one and number two against each other.
"We just have to prepare ourselves very well and focus again now."