Holders Barca were dumped out of the King's Cup by their arch rivals on Tuesday, suffering a humiliating 3-1 semi-final second leg battering in front of their own fans, to miss out on a place in the final.
With the defeat coming hot on the heels of their lame 2-0 Champions League last 16 first leg reverse at AC Milan last week, alarm bells have been ringing at the Nou Camp as Barca's season threatens to run out of steam.
Pep Guardiola's former assistant had a tumour removed from his glands in November 2011 and is not expected to return until mid-March.
"It isn't easy without the presence of the first-team coach," Barca and Spain midfielder Andres Iniesta told a news conference on Wednesday.
"It's been a long time and it's one more hurdle we have had to get over this season.
"We don't need him to return immediately now we have lost a couple of games. His health comes first, and we have confidence in those who are here."
"We need to think hard about the two games we have lost, what we did well and where we can improve," Iniesta added.
"We need to recover the sensation of being a compact and infallible team and I am convinced we can do this.
"We shouldn't forget we are leaders in La Liga and we should try to maintain our advantage."
Real will be without suspended winger Angel di Maria for a 'Clasico' overshadowed by their trip to Old Trafford.
A readers' survey on the Madrid-based sports daily AS website on Thursday saw fans voti
