The ref was struck after blowing the final whistle as Espanyol were beaten at home by Villarreal.
Quintero González wasn't injured and stood his ground while pointing out the person who threw the cup until he was detained.
Afterwards, Espanyol coach Manolo Gonzalez said: "I couldn't see what happened. I was upset and I went to the locker room so as not to run into anyone.
"I don't want to talk or say anything. I'm focusing on the sporting issue. I hope they don't close the stadium."
In his match report, Quintero Gonzalez stated: "Once the match was over, we were at the entrance to the changing room tunnel when a medium-sized plastic cup filled with liquid was thrown towards me, hitting my chest with force.
"The object was thrown by a fan wearing a shirt of the local club from above the tunnel. In response, I requested the identification of the individual by the security forces, which was positive, as the security coordinator informed me. Once in the changing room, I was assessed by the medical services of the local club, who assessed that there was no apparent injury."
Espanyol have stated the club "condemns any act of violence" and has collaborated after what happened to quickly arrest the spectator and hand the person to local police.