Madrid - Spanish coach Manuel Preciado died of a heart attack in Valencia aged 54 on Thursday, his former club Sporting Gijon said in a statement on their website.
Preciado had on Wednesday agreed a deal to take the reigns at relegated Villarreal for next season and was scheduled to be presented at the Madrigal on Friday.
"Sporting Gijon convey their great sadness for the loss of someone who wrote their name in our history in golden letters, and send their condolences to his family in these painful moments," the relegated club said.
The popular and charismatic Cantabrian, had coached Sporting between 2006 and January this year, when he was sacked after a poor run of results.
He had been the second longest-serving coach in Sporting's history, after having also worked with Racing Santander and Levante among others.
Villarreal, who had been looking to Preciado to lead them back in to La Liga next season after he successfully guided Levante and Sporting into the top division, said: "Villarreal wish to show their deep sorrow for the sad loss."
Tributes quickly appeared in the local media, one of the first coming from the Spanish national team coach Vicente del Bosque in Poland, where the team are preparing to start the defence of their European championship title.
"He was a man of football who represented the best values of his profession," Del Bosque told Marca Radio.
"He was a fighter who leaves a large gap in this world," he added of a man who had lost his wife to cancer and a son in a road accident.
Spain midfielder Cesc Fabregas wrote on Twitter: "I can't believe the bad news I just woke up with. Hugs for the family of Manolo Preciado. RIP my friend."