Sporting Lisbon president Frederico Varandas says Manchester United will have to offer more than £56m for Bruno Fernandes.
Reports in Portugal last week claimed United were prepared to offer £50m for the 24-year-old.
But Varandas insists Sporting won't accept any less than their valuation.
"I don't know if there are many or if there are few [interested clubs]," Varandas told RTP at Lisbon Airport.
"What I know, a lot has been spoken of values, coming to the press, €55m, €62m… for that he doesn't leave, for sure.
"If Bruno Fernandes leaves, players with quality will come. But if Bruno leaves."