Real Madrid coach Jose Mourinho led the tributes for Manuel Preciado, who died on Thursday morning just a day after being named as the new Villarreal coach. He was 54.
Relegated Villarreal announced on Wednesday they had reached an agreement for Preciado to take charge of the club next season as they sought an immediate return to the Primera Division.
Preciado, who had parted company with former club Sporting Gijon in January, had been set to be presented as the Yellow Submarine's new manager on Friday lunchtime, but then the news broke that the Cantabrian had died of heart attack overnight in Valencia.
Villarreal president Fernando Roig said: "He was a great person for football. We are going to support his family and try to help them at this difficult time."
Tributes have been pouring in from the Spanish footballing community for the popular Preciado - known as Manolo - with Mourinho writing an open letter on the Real Madrid website.
In his letter, Mourinho said: "Manolo was always an honourable opponent, who I got to know well when he came to visit us in March,
"He had everything that I like in a person and in sportsmen: character, openness and the courage to fight against blows. We have been left by a football figure and above all by a very special person. My memory of him will be heartfelt and permanent."
Sporting, who were relegated in the recently-completed season along with Villarreal, said on their website: "With deepest regret, Sporting Gijon wish to express their sorrow at this sad loss, for someone who formed an integral part of this club's history, and send their deepest condolences to his family in this time of grief.''
National team coach Vicente Del Bosque, whose side are preparing for their Euro 2012 opener against Italy on Sunday, told Radio Marca: "We're shocked. We were having breakfast and it made a deep impression on us.
"He was a football man who represented the values of this sport. He was a fighter who made his mark in this world."