Liverpool have asked Sporting about a player with just nine first-team appearances to his name, according to Record.
But the Portuguese newspaper claims Liverpool were told to pay €45 million (around £40.1m) to get him.
Nuno Mendes is a product of the same Sporting academy system that spawned Luis Figo, Cristiano Ronaldo and Nani.
And big things are also expected of Mendes, after his impressive run in the side between early June and the end of July.
The left-back has already been linked with moves to Liverpool and Manchester United, but it is the Merseyside club who appear to have made first contact.
Whether or not Liverpool will follow up their interest remains to be seen, however, with the Reds having already strengthened in Mendes’s position through the acquisition of Kostas Tsimikas from Olympiacos.
It is thought that Tsimikas will begin his Anfield career as understudy to Andy Robertson, one of the stars of Jurgen Klopp’s team.
Mendes can, however, operate in a more advanced role if required, and filled in at centre-back against Santa Clara last season.
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