The Spanish custodian has dropped to fourth choice under Sir Alex Ferguson at Old Trafford, and only recently hinted he may depart to gain more first-team football.
Ricardo travelled to the Cantabrian club on Friday and swifty agreed terms with Racing, who are early contenders for the drop in La Liga this season.
While United will still pay 25 percent of the keeper's wages, Ferguson will undoubtedly be pleased to offload a player who was unlikely to feature in his squad this season.
The Spaniard hinted on Thursday his future lay away from the Premiership champions, after falling to fourth choice following the arrival of US international keeper Tim Howard from the New York/New Jersey MetroStars.
