The Portuguese came to watch Dortmund beat Greuther Furth 6-1 on Saturday and the 45-year-old says his side showcased all of their qualities
The deposed German champions clash with los Blancos in the Champions League semi-finals later this month and the Portuguese went to see his side's opponents in action on Saturday.
BVB triumphed 6-1 at the Trolli Arena and the former Mainz coach feels Mourinho's exit when the visitors were 5-0 up means he did not see anything useful.
"We are no longer in the situation where we want to play well for Mourinho. He will have got some impression, which he cannot use in two weeks, because everything will be different," he told Sky.
"But if he wants to see Furth, he is welcome ...
"He left after the 5-0 and didn't see our weaknesses. But if he wanted to see whether [Mario] Gotze can play on the left, he can call me."
Gotze and Ilkay Gundogan netted two goals apiece, with Jakub Blaszczykowski and Robert Lewandowski also getting their names on the scoresheet in the eventual 6-1 win.
BVB host Madrid on April 24 before travelling to the Santiago Bernabeu six days later.