The 27-year-old, who joined the club in September 2012, had been expected to sign a new long-term contract with the Premier League club.
However, his agent Sebastien Casenaz told talkSPORT: "We have not reached an agreement with Swansea. Dwight has been very good this season and the caps he earned with the Dutch national team came as a reward for his performances on the pitch with Swansea.
"As a free agent, of course Dwight is attracting interest from clubs in England and Germany. Currently, discussions continue."
It is understood that the Dutchman is keen to remain in the Premier League.