The Bavarian giants are bidding to become the first team to defend Europe's premier club competition since Milan did so in 1990.
Pep Guardiola's men secured the Bundesliga crown last month, allowing them to turn their full attention to lifting the Champions League trophy once again.
Nine-time winners Real – who will be hoping key men Cristiano Ronaldo and Gareth Bale are passed fit - do not have the same luxury and are involved a three-horse race, with city rivals Atletico and Gerardo Martino's Barcelona, for La Liga glory.
Real were not in action at the weekend, but Bayern beat Eintracht Braunschweig 2-0.
Captain Philipp Lahm felt that win, which came after back-to-back Bundesliga defeats, was crucial ahead of their crunch clash in Madrid.
"We did very well, especially in the second half. It's important we set off for home feeling good, and that's exactly what we're doing," Lahm told the club's official website.
"(Against Real it will be) sensational. I'm really looking forward to it. We'll see two massive games.
"On Wednesday we'll show we're always up for it in the important games. But it's still 50-50."
Bayern, who have won the competition five times, are set to welcome Manuel Neuer back from a calf problem after the Germany goalkeeper missed the last two matches.
The 28-year-old participated in training on Sunday and is expected to be fit, while David Alaba should be available after missing out at Braunschweig due to illness.
Bayern will have happy memories of facing Real in the Champions League, with a 3-1 penalty shootout win securing their place in the 2011-12 final.
The Germans won the first leg 2-1 thanks to goals from Franck Ribery and Mario Gomez, and although Ronaldo struck twice in the early stages of the second leg, an Arjen Robben penalty forced extra time.
The tie was eventually decided by a penalty shootout, with Neuer Bayern's hero as he saved from Ronaldo and Kaka, while Sergio Ramos' miss allowed Bastian Schweinsteiger to strike the winning penalty.
The two sides have met five times in the semi-finals of the competition, with Bayern winning four – in 1976, 1987, 2001 and 2012 – while Real's sole success came in 2000.
Real have not won the competition since 2002, but will take heart from the fact they are unbeaten in their last 17 home matches in Europe.
In fact their last Champions League defeat at Santiago Bernabeu came when Guardiola steered Barcelona to a 2-0 success in the 2010-11 semi-finals.
Real coach Carlo Ancelotti will be sweating on the fitness of Ronaldo and Bale, although the former has returned to full training.
Ronaldo has missed Real's last four matches due to knee and thigh problems, but came through a training session on Monday.
Bale is suffering from illness and it would be a major blow if either player is ruled out.
Defender Sergio Ramos should be fit, having recently been troubled by a neck injury.
Bayern are unbeaten in their last 10 away Champions League matches and know if they can extend that run they will take a big step towards next month's Lisbon final.
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