The Paraguay international's prolific record for the Portuguese giants has attracted interest from a variety of clubs, including Cardiff City, Spartak Moscow and Zenit St Petersburg.
Spartak have denied making an €18m bid for the 30-year-old, who scored 26 times for Benfica last season, while Cardiff boss Malky Mackay has admitted to being an admirer of Cardozo's talents.
Talks over a move to Fenerbahce fell through, but the player is adamant that his future lies away from the Estádio da Luz.
"I thank the fans for always being with me," Cardozo told A Bola.
"But, after everything that has happened, it will be very hard to find motivation to continue. My head is far away from Benfica."