Porto are reportedly unprepared to sell midfielder Vitinha for anything less than his £34m release clause.
After Wolverhampton Wanderers failed to take up their option to buy the player last summer, Vitinha has gone on to star in the centre of Porto's midfield.
The 22-year-old has made 33 appearances in Primeira Liga and European fixtures, inevitably leading to widespread interest in his signature.
Nevertheless, according to Defensa Central, Porto will not cash in on one of their most prized assets unless his release clause is activated.
Liverpool and Real Madrid are said to be monitoring the situation as they consider freshening up their options in the middle of the park.
Vitinha has recently been called up to the Portugal senior squad, enhancing his reputation in the process, and it may lead to Porto attempting to renegotiate his contract.
