The former Netherlands international says his men will be searching for a victory at Santiago Bernabeu so that other results cannot affect their Europa League spot
The Amsterdammers go into the fixture in third place and cannot of break into the top two, but, a win will mean they secure a Europa League spot, ahead of Manchester City, who are currently bottom of the group.
The Ajax coach is determined to ensure that they are not disappointed come Tuesday night.
"The most important thing for me is that we are going to see a good Ajax performance. We have to win so the match in Dortmund doesn't matter," De Boer said in a press conference.
With Los Blancos already through to the knockout stages and unable to win their group, Jose Mourinho is expected to rest some of his senior players, something which De Boer does not believe makes a difference to the size of the task ahead.
He added: "When you see which players are still in the line-up, you cannot really say that Real have been weakened but I just hope that the win against PSV [at the weekend] has given us a boost."
Ajax goalkeeper Kenneth Vermeer was also present at the press conference, and was in a positive mood when asked whether or not he thought that his side could win the game.
He said: "Why not? Against Manchester City we played really well in both games. Of course I want to go through in Europa, the level is still a very high standard."