The Yorkshire Evening Post understands that Leeds have already received a tentative enquiry from Old Trafford about Viduka's availability.
Leeds would resist any approach for the Aussie, but Eddie Gray admits he won't be surprised when other clubs come knocking on his door. Inter Milan were also mentioned today as an interested party.
Gray confirmed: "You can never tell what happens with players. I'm sure Viduka is a player who will attract interest from other clubs.
"In an ideal world you would want to keep him. It's important you keep all your best players, but you have to be realistic enough to know that things change.
"Everybody in the game knows he is a world class striker, one of the best
in the business, but it's something I'm not thinking about at the moment.
"He's in good form at the moment. He knows what he's about, he just gets on with it. I just tell him what I expect.
"He is a great player. He holds the ball up and brings people into the game. That's his job.
"I've got great faith in his ability. Anyone who has worked with him will know about his talents."