Iago Aspas has been banned for four games after being sent off for his headbutt on Deportivo's Carlos Marchena during Celta Vigo's 3-1 away defeat in the Galician derby last Friday.
Aspas, 25, is now set to miss his relegation-threatened side's vital upcoming Primera Division clashes with Barcelona (home), Rayo Vallecano (home), Real Mallorca (away) and Real Zaragoza (home). He was also fined €3,005.
Celta had made a representation to Spain's disciplinary committee, claiming Aspas had been provoked by the more experienced Marchena, who had not been injured in the incident.
However, the authorities stuck to the referee's decision that it was a case of serious aggression that merited a significant punishment.
"This is an obvious case of aggression," a statement read. "The circumstances brought up by the club do not change the seriousness of the offence."
The club said via their website they would appeal the decision, which is a huge blow for their survival hopes, but are unlikely to be successful. Abel Resino's side are currently 19th in the table, only three points from safety, but in wretched form with just three points from their last six games.
Aspas, who is rumoured to have already agreed to join Valencia in the summer, has scored ten and assisted six of his side's 27 La Liga goals this season. His replacement could be on-loan Arsenal forward Park Chu-Young, who did score against Depor but has only four goals in 22 appearances, mostly as a substitute, for Celta this term.