The German giants are through to the Champions League semi finals, where they will play Paris Saint-Germain.
Dortmund beat Atletico Madrid over two legs, with United loanee Jadon Sancho playing in both games.
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The loan deal saw Dortmund paying an up-front fee of 3.5 million, along with a further 4 million in potential add-ons.
Part of the deal, per the Manchester Evening News, involved Dortmund's European performances.
They will earn even more if they make the final or go on to win the competition.