"Jose Mourinho will not answer any question," a club spokesman said at the start of the news conference, causing many journalists to abandon Real's press centre in protest.
Karanka was left to justify the Portuguese coach's decision to remain mute.
"Every time he speaks, everything he says gets magnified, he does not want his words to be magnified," he said as a stony-faced Mourinho sat beside him and faced the journalists who stayed at the press conference.
Real will face Barcelona at home on Saturday in the league ahead of three more 'Clasicos' in less than three weeks, in the Spanish Cup final and the Champions League.
Champions Barcelona hold a commanding eight point lead over Real in the league with seven games left and victory over their foes would virtually seal the league title, while a draw would still leave Madrid with a mountain to climb.
Mourinho watched Sporting Gijon win 1-0 at the Bernabeu in their last home league outing to end his nine year 150 match unbeaten home league record and the Portuguese hopes to fare better than in his first Clasico when Barcelona thrashed his side 5-0 at Camp Nou.
It was the heaviest defeat of Mourinho's glittering career and both he and his wounded players will be out for revenge for that humiliation.