Sporting Lisbon are reportedly keen to increase the release clause of Gelson Martins from £53m to £89m as they look to protect their investment in the in-demand winger.
Martins, 22, came through the youth system at Sporting, and has since developed into a key player for the Portuguese club.
The attacker scored 14 times in his first three seasons with Sporting, but has already managed nine goals and seven assists in all competitions during the 2017-18 campaign.
Real Madrid have previously been credited with an interest, while Liverpool are also said to be monitoring developments surrounding a player that has represented Portugal on 15 occasions.
According to Record, Sporting president Bruno de Carvalho is aware of the interest in Martins, and the 45-year-old is keen to raise the attacker's buy-out figure to £89m.
Manchester United boss Jose Mourinho is also believed to be an admirer of his fellow Portuguese.
