Real Madrid will play their Primera Division home clash against Barcelona on the afternoon of Saturday, March 2.
That will give them three days to prepare for the second leg of their Champions League clash with Manchester United.
Madrid had reportedly been hoping to stage the match on the Friday in order to give them extra time ahead of their last-16 return trip to Old Trafford, the first leg of which takes place on Wednesday night at the Bernabeu.
However, the kick-off time has now been confirmed by the LFP (Spanish football league) as 1600 local time on March 2, which is the same time as United are scheduled to start their Barclays Premier League home match against Norwich.
That means the season's second La Liga El Clasico is unlikely to be screened live on television in the UK due to a clash with domestic fixtures.
Four days prior to hosting Barca in La Liga, Madrid go to the Nou Camp for the second leg of their Copa del Rey semi-final in what promises to be a crucial period for Jose Mourinho's men.
The 19-year-old is in the last couple of weeks of his loan deal and has impressed at Kingsmeadow.
After he was sent-off on his debut, McCallum bounced back to score four goals in the space of three games for the struggling Dons in January.
The youngster is thrilled with how his loan has worked out and wants to boost Neal Ardley's side's survival hopes before he returns to the Hammers on February 23.
He told the club's official website: "It (January) was a great month for me as I was starting games and scoring goals to help Wimbledon do really well.
"I got the winner against Rochdale and then two goals against Wycombe Wanderers. I maybe should have scored more goals in that game to help us to victory, but that's the way it goes as a striker.
"I expected to maybe score a couple of goals during my spell at Wimbledon, but not four goals in three games.
"Hopefully, I will get a chance to start again and get a couple more to help the club move away from the relegation zone."
