Fuentes was once an athlete. He then became the team doctor of Team ONCE, Amaya and the Kelme. The former Kelme rider Jesús Manzano accused Fuentes of being involved with doping. Fuentes retired as the team doctor of the Kelme team in 2005. At that time he had been the doctor of the Kelme team for 16 months. He announced that he was retiring from involvement with professional cycling, citing health and family reasons as well as a desire to investigate retinoblastoma cancer in the Instituto del Cáncer de Canarias.
Fuentes was arrested by the Guardia Civil on May 22, 2006 together with four others: the manager of the Liberty Seguros team Manolo Saiz, José Luis Merino a haematologist at an analytical laboratory in Madrid, Alberto León, a professional mountain biker, and José Ignacio Labarta, who was at that time the assistant sports director of Comunidad Valenciana.