The Spanish side caused a seismic upset when they beat Manchester United in the last round and it will take a display similar to their win at Old Trafford to get the better of the Germans on Wednesday night.
However, Heynckes said both left-back David Alaba, back in training after a back injury, and midfielder Arturo Vidal, who has a knock, are unlikely to play.
Pressure is mounting on head coach Vincenzo Montella after some ropey defending at Vigo.
"I know who will play but I don't want to reveal it until tomorrow", Montella said.
Real slipped down to fourth in the Liga standings and 15 points behind leaders Barcelona following Sunday's draw with Atletico Madrid.
The last two UEFA Champions League semi-finalists will be decided on Wednesday as the quarter-finals come to an end.
"I don't have an explanation".
"We had some hard moments, especially with scoring goals".
That's pretty good going in anyone's book both for longevity and just for sheer amount of success, and those lads very much have Sir Alex Ferguson to thank for having to spend a lot of money on trophy cabinets.
Juventus will take the field against Real Madrid at the Santiago Bernabeu knowing they will have to do something unprecedented to advance to the semi-finals of the Champions League.
Cristiano Ronaldo's reigning champions bring three away goals home from Turin, and it's hard to believe even a club as storied as Juve can collect a three-goal win given the opposition and the venue of the Bernabeu.
"We know we can score a goal or two in the second half, but we have to avoid conceding, especially in the second half".
"Winning the league makes me more excited, it's the most hard competition and I also think it's what the players want".
With Bayern already wrapping up the Bundesliga title, they will be able to fully divert their attention to winning the Champions League for the first time since 2013. "The important thing is to remain in the game, to have balance, be patient".
"It will be a hard game against a great team", said the French defender.