The 23-year-old has also been linked with Manchester City and Tottenham.
The former Chelsea star will join Real for around £9million.
“The big players are already in the Champions League and cannot be signed,” Ramos is quoted as saying.
“If the players do not have the quality, then we will miss them – the players have to be worth it.”
And on Diarra he added: “He is a player I know well, and I would like a player like Diarra here.”