The 24-year-old was a vital cog in the Partenopei machine last season, netting seven goals in 47 games in all competitions.
His impressive showings in Serie A led to interest from Los Blancos, as well as Liverpool and Man City, but Napoli remain adamant that the player is happy at Stadio San Paolo.
The Poland international recently penned a new contract in Italy which includes a €120 million release clause.
The 23-year-old is one of European’s most promising young players and is being viewed as a long-term replacement for the ageing Fernandinho at the Etihad Stadium.
Dortmund are keen to keep hold of the youngster but could be resigned to losing him if City put their full weight behind a transfer bid in the January transfer window.
Barcelona are interested in signing Sassuolo star Domenico Berardi, according to Sport.
The Catalan giants are seeking fresh faces in January after failing to recruit a big-name striker this summer.
But with manager Ernesto Valverde targeting success on both La Liga and Champions League fronts, more attacking flair is required at the Camp Nou.
Berardi, 24, has been the subject of interest from some of Europe’s top clubs, and Barcelona are ready to prepare a bid before other clubs nip in ahead of them.
It is believed the Italian international, who has scored 60 goals in 182 appearances at Mapei Stadium, would be available for around £22m-£27m