The veteran Dutchman has been engulfed in controversy over the last 48 hours, following reports that he was eager to force his exit from current club Hamburg in order to return to Spain.
He is in the line-up as HSV meet Schalke in the Bundesliga, but nonetheless Jose Mourinho remains enthusiastic about the idea of retaining the ex-Manchester United star's services.
"It would be great if we signed another striker," he told the press. "The club's now opened the door to this and that pleases me. But we need to be patient as there's plenty of time before January 31. The sooner we sign someone, the better.
"If it was Ruud van Nistelrooy I would be very pleased. He's a player that I know very well from the Premier League."
Van Nistelrooy Looking To Leave
HSV coach Armin Veh has acknowledged that Ruud is eager to return to the club where he scored 46 league goals in 68 appearances.
He told the German media, "Officially, Real Madrid haven't made an offer. They want him - we know that, because Ruud told me this. But officially there's no offer.
"The club has to decide what happens - it's not down to the coach."