Dutch striker Ruud van Nistelrooy is being linked with a move to either Real Madrid or Barcelona.
Reports suggest both clubs are prepared to pay up to £30m for the striker and believe United will sell at the right price.
Madrid-based newspaper Marca believes Real have already agreed a deal “in principle”.
Earlier this week, Barcelona vice-president Ferran Soriano has the club had the resources to buy the striker.
He stated: “The club will be able to spend £33-40m on acquisitions. All is possible, even Van Nistelrooy.
“There is not any player who is out of our market, only ones that their clubs will not sell, such as Thierry Henry – just like we would not sell Ronaldinho.”
Madrid president Florentino Perez is believed to have met with the Dutchman’s agent, Roger Linse, within the last month.
Moreover, Real’s sporting director Jorge Valdano is a confirmed admirer of the former PSV striker.
“A player like Van Nistelrooy would have a place in any team in the world, including Real Madrid – who would not want to sign him?” said Valdano in December.
United have consistently denied the rumours lining the forward with a move away from Old Trafford.
“Ruud is not for sale,” said a club spokesman.
“We have said this consistently, so I don’t know what more we can do.
“He signed a new contract in January and has said himself over the last few days that he wants to stay with the club.”