Villarreal coach Manuel Preciado died of a heart attack Thursday, one day after joining the team. He was 54.
The team said Preciado was in Valencia when he was stricken early Thursday.
"We are all shocked," Spain coach Vicente del Bosque said from Poland, where he is preparing his team for the European Championship.
"We were having breakfast and we were all taken back by the news," he told Spanish radio Marca. "He was a caring person and a great sportsman. He was a man of football that was an honor to coaching."
Preciado played for several clubs, including Racing Santander, and had previously coached teams including Racing Santander, Levante, Murcia and Sporting Gijon.
He had a one-year deal at Villareal, which was relegated from the Spanish league last season.
Villarreal's website said the team had expressed its condolences to Preciado's family.
Preciado's death led to an outpouring of support from Spanish clubs, coaches and players.
"We all burst into tears on hearing the news," Mallorca coach Joaquin Caparros said. "I was so happy for him joining Villarreal. I am sure he would have taken it back to the first division."
A native of the Cantabria region in northern Spain, Preciado began coaching in the third division in 1995. He led Levante from the second to the first division in the 2003-04 season, and also guided Sporting back to the top flight for the first time in 10 years in 2007-08.
He coached Sporting for five and a half seasons before a poor start last year led to him being fired midway through the season. Sporting did not recover and was relegated, along with Villarreal and Racing.
While never finishing better than 10th in three seasons, Preciado's modest Sporting dealt Madrid manager Jose Mourinho his first home loss in league play in nine years through an unexpected 1-0 victory at the Santiago Bernabeu in April 2011.
Preciado was a fan favorite in Gijon and one of the most charismatic managers in Spain, known for his frank and entertaining manner of addressing the media and players alike.
Preciado's 232 games for Sporting was second only to Jose Diaz Novoa's 282. Sporting said Preciado's name was "written into the history of the club in golden letters."
As a player, he also had stints with Mallorca, Alaves, Ourense, Linares and Gimnastic de Torrelavega.