Former Real Madrid director general Jorge Valdano says Jose Mourinho would only be classed as a great coach if Pep Guardiola did not exist.
Valdano, a former Madrid player, coach and sporting director, held his most recent position with the club for two years until he was sacked in 2011 after his relationship with Mourinho deteriorated and he lost the resulting power struggle.
The 58-year-old has taken a fresh swipe at the Chelsea manager, saying the Portuguese had nothing worthwhile to say about football and suggesting he falls short of Bayern Munich boss Guardiola - the coach of Madrid's bitter rivals Barcelona for the first two years of Mourinho's stay - by comparing him to Italian composer Antonio Salieri.
Writing in his book 'The Eleven Powers of the Leader' Valdano said: "If Guardiola is Mozart, then Mourinho is Salieri. He would be a great musician if Mozart did not exist.
"Mourinho is a personality made for these noisy and empty times. I never heard him say something about football, in public or in private, that was worth remembering.
"I could never understand him as we were coming from opposite poles. Intelligence and egos are enemies - when they clash, the ego wins."
Valdano expanded on the comments in his book during an interview with El Larguero, admitting that Mourinho's methods do get results but that his biggest failure was his lack of Champions League success in three years with Madrid.
He said: "Mourinho is a professional, passionate and winning coach but his thinking on the game is very different than mine. He is much more interested in results and he often gets them.
"But he had one of the best squads in the history of Real Madrid and always remained just outside the door of the Champions League. That was the big challenge which he did not manage to succeed at.
"I have not heard from Mourinho's camp about my book - I do not have a close relationship with them."