Cuper managed to lead the Spanish side to just one victory in their opening 13 Primera Liga games this season.
Cuper told his squad about his exit before training on Tuesday.
Danish legend Michael Laudrup has been linked with the job as Racing Santander boss.
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The reputation of the Premier League means it is the most popular and one of the most watched leagues in the world.
Five English clubs will compete in the last sixteen of the Champions League for the first time ever as Liverpool, Manchester United, Manchester City, Chelsea and Tottenham face some difficult away matches.