With Kaka choosing '8' as his number, Raul Albiol picking up the No.18 shirt and Cristiano Ronaldo the famous No.9 jersey, there were no available options for the 21-year-old striker, who was presented in a numberless shirt.
Benzema will have to wait for one of his team-mates to depart the club to have a number at his disposal, with Klaas-Jan Huntelaar's No.19 shirt being a likely option.
Real Madrid chairman Florentino Perez introduced Benzema as "the best young player in the French league", with the striker then thanking the opportunity to play at "the best club in the world".
"I am very happy to play in the same club as my idols, Zidane and Ronaldo. Thank you Florentino Perez," he added.