Valdano was forced out of Real by Mourinho this summer.
"Let's say that what happened does not exactly honour Real Madrid or Mourinho. I am convinced no-one is proud about what happened," Valdano told ADN Deportes.
"Mourinho came to a club with 109 years of history and of course he represents a club with a very solid culture. What happened is that in these moments the tension between Real Madrid and Barcelona is so high that everyone is overcome by the pressure."