We have a chance for Riquelme only because Riquelme has openly stated that he would like to play for Manchester United in the past. That, and <s>I think</s> his club has not qualified for the CL next season, something which is also working against Athletico (who have Torres), who haven't even managed to make the UEFA Cup.

EDIT: On a quick check, Riquelme's current club Villarreal haven't made the UEFA Cup, either.