Porto have set a €75m (£67m) asking price for centre-back Eder Militao, according to Portuguese newspaper O Jogo.
The usually reliable publication says that Real Madrid are the frontrunners for the Brazilian, although Manchester United are also reportedly interested in the 20-year-old.
Porto are reluctant to let Militao leave during the January transfer window so they have opted to place a premium on any club looking to purchase the defender this month.
If a club comes back in for the player in the summer, however, the centre-half could be available for the much lower fee of €50m (£45m).
Whether either price would attract United, it isn’t known. Militao only moved to Portugal from Sao Paulo at the beginning of the season and is yet unproven in a top European league.
The Manchester club are believed to be very keen to bring in a new face at centre-back. There are cheaper options out there with Roma’s Kosta Manolas, a reported target, said to have a €36m (£32m) release clause.