Van Wolfswinkel, who joined Sporting from Dutch side Utrecht in June 2011, has scored 29 goals in 53 matches since moving to Portugal.
Tottenham have been linked with a January move for the striker, while Liverpool and Newcastle are also believed to be admirers of the Dutchman.
But while his agent, Louis Laros, admits there has been outside interest in the 23-year-old, he says the frontman is close to extending his stay at the Estadio Jose Alvalade.
Laros told Portuguese newspaper O Jogo: "The conversations with Sporting's directors are very advanced and I expect news in the next few weeks."
Asked about interest from other clubs, he added: "Yes. There are always clubs asking about the footballer but Ricky is happy in Lisbon and at Sporting.
"He has still not fulfilled the challenges at Sporting and it is his desire to follow them.
"For that reason we are working on a new deal.
"It is practically impossible he leaves in the January market."