Eldense coach Filippo Vito di Pierro has been arrested after the club's 12-0 defeat to Barcelona's "B" team.
Di Pierro was detained in the small eastern city of Elda on Monday by Spanish police investigating claims of alleged match-fixing.
The Italian, who was acting as one of Eldense's coaches alongside Fran Ruiz Casares, was hired in January by an unnamed Italian investment group which managed the club's sporting and financial affairs until Sunday.
Authorities detained him after interrogating some Eldense players following a complaint made by the club's president.
Eldense ended its contract with the group of Italian investors and temporarily ceased its sporting activities on Sunday, a day after the record-equalling defeat sealed its relegation.
"This is a very delicate subject and it needs to be treated very seriously," said Barcelona coach Luis Enrique.
"In other countries we have seen similar situations and they are very unfortunate. Too many people are trying to benefit from football."
The 12-0 loss equalled a record for Spain's third division - Extremadura routed Portuense by the same score in 1993.
Di Pierro has denied any wrongdoing while there is no indication that Barcelona B players had any involvement with the alleged match-fixing.