The 22-year old Belgian has become a strong target for United boss Sir Alex Ferguson who is prepared to pay £13million for him.
Ferguson has been tracking Defour for more than 12 months now which his agent, Paul Stefani, confirmed.
"Sir Alex has been interested in Steven since he sent him the letter last September when he was struggling with injury," Stefani said.
"He is still interested but we have to wait for an offer to be accepted by Standard Liege.
"There is also interest from clubs in Spain, Italy and Germany, but everyone wants to play in the Premier League."