Real Madrid must choose between new signings Klaas-Jan Huntelaar and Lassana Diarra to play in the knock-out stages of the UEFA Champions League, UEFA spokesman William Gaillard said on Spanish radio.
"I am very sorry, but the rules are what they are and they cannot be changed in the middle of a season," he said on Onda Cero radio. "That means that only one of the two players can play in the Champions League. They can include either Huntelaar or Diarra."
The Spanish champions, plagued by injuries and poor form this season, signed Dutch striker Huntelaar and French midfielder Diarra this month from Ajax and English side Portsmouth respectively. But under UEFA rules only one of them can play in the Champions League as both have have already represented their former clubs in Europe this season.
Real had hoped to convince European football's governing body to agree to a different interpretation of the rule so that both players could take part.
The club has been drawn against Liverpool in the Champions League first knockout round on 25 February and 10 March. The club, who are fifth in the Spanish title race some 12 points adrift of Barcelona, have suffered season-ending injuries to key players Dutch striker Ruud van Nistelrooy and Malian midfielder Mahamadou Diarra.
UEFA rules for the 2008-09 season state that a club may register up to three new players for the knockout stage of the Champions League. But only one of these can be a player who has represented his former club in Europe, and provided it was in another European competition. Both Ajax and Portsmouth were competing in the UEFA Cup this season.