Raul Bravo, a full back for Madrid who also had a brief spell on loan at Leeds United, is reportedly the head of the alleged group.
Saiz, on loan from Leeds at Getafe and LaLiga player Borja Fernandez of Valladolid have also been questioned according to police sources, claims news outlet Servimedia.
Also said to be involved are Carlos Aranda, who previously played for several LaLiga clubs, and Inigo Lopez, of second tier side Deportivo La Coruna.
Huesca president Agustin Lasaosa and club doctor Juan Carlos Galindo have been questioned by police who raided club offices.
The police operation into illegal sports betting began on Tuesday morning.
A spokesman for Spain’s National Police confirmed an operation is “ongoing”
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