The midfielder is considering his future after Rafa Benitez registered his interest in his services
Rafa Benitez has registered his interest in securing the services of the 23-year-old, who featured in the World Cup final as Germany lifted the trophy in Brazil.
He told Bild: "There is contact with Napoli. The offer is interesting, especially because Rafa Benitez is the manager and he is a great coach.
"At the moment I cannot say anything else. I could go back to Borussia - there are many possibilities.
Kramer spent last season on loan at Borussia Monchengladbach, with his impressive displays seeing him emerge as one of the Bundesliga's top young talents.
He covered more ground than any other player in the division and capitalised on injuries to Ilkay Gundogan and Lars Bender to secure a place in Germany's World Cup squad.
His current deal with Leverkusen runs until June 2015 and therefore he could be available for as little as €10 million.