A day after being appointed coach of recently relegated Spanish side Villarreal,
Preciado, 54, had been due to be officially unveiled as Villarreal's new coach on Friday.
"A heart attack claimed the life of Manuel Preciado in the early hours in Valencia," his former side Sporting Gijon said in a statement.
"Villarreal want to express their deepest sorrow at the sad loss and want to offer their condolences to his family and all his relatives," Villarreal added in a statement.
Villarreal turned to Preciado to try and help earn the Yellow Submarine an immediate return to the Primera Liga after its drop to the second tier.
Preciado left his post as coach of Sporting Gijon in January after six years in charge of the Asturian club.
Giuseppe Rossi is dreaming of a return to UEFA Champions League football after completing his move to Fiorentina for an undisclosed fee.