During his negotiations to bring Gyokeres to Sporting in a £20m deal from Coventry City two years ago, the striker’s agent, Hasan Cetinkaya secured an exclusive sales mandate which means that the Portuguese champions will have to pay the agent 10 per cent of the value of any rejected offer above €60m (£51m).

Viktor Gyokeres has been at the centre of a transfer battle this summer, with Manchester United and Arsenal both interested in signing the Sporting striker.