Former Barcelona midfielder Andreas Iniesta has claimed Jose Mourinho created an unbearable atmosphere between Barca and Real Madrid players when he was in charge at the Santiago Bernabeu.
Iniesta called time on a glittering career with the Catalan giants at the end of last season and now plays for Japanese side Vissel Kobe.
Mourinho developed a fierce rivalry with Barca boss Pep Guardiola while he held the hot seat at Real from 2010-13. Meanwhile, the Spain international team started to decline after their victory at the 2012 European Championships, crashing out of the 2014 World Cup in the group stages.
Speaking about the animosity between the two Clasico teams, Iniesta told La Sexta : "You don't have to be for Barcelona or Real Madrid to know that the situation was unpleasant.
"And the key component in that story was Mourinho. Whoever doesn't want to see that, is radical.
"You didn't see the rivalry that always existed before, it went beyond that, you saw hate. That atmosphere developed and it was unbearable.
"The Barca-Madrid tension caused by Mourinho did much damage to the national team [Spain] and the teammates."
Mourinho has since reignited his rivalry with Guardiola in England, the two managers taking over at Manchester United and Manchester City respectively in 2016.
Their war of words has continued, with the Red Devils boss often referring to the amount of money his opposite number has had to spend, saying in August, "You cannot buy class."
Mourinho has also drawn criticism for creating a negative mentality among his own players, Rio Ferdinand most recently criticising his comments about Luke Shaw, Marcus Rashford, Anthony Martial and Jesse Lingard.
Speaking in the build-up to his team's goalless draw with Crystal Palace, Mourinho said the quartet lack maturity. His handling of other players has also been questioned, with particular scrutiny being aimed at the fallout he had with former vice-captain Paul Pogba.