The deal could include Tottenham playing two friendlies with the Portuguese side.
The Portuguese international may take part in the Carling Cup semi-final against London rivals Arsenal on Wednesday at White Hart Lane.
Spurs sporting director Damien Comolli said: “Ricardo is an accomplished defender who gives us further options and brings considerable experience.
He added: “He has played at the highest level in European competition and is also a current Portuguese international.
“Ricardo has shown a great desire to come to White Hart Lane and will no doubt prove to be a valuable addition to the squad at this important time.”