Van Wolfswinkel agent claims relegation clause
The 24-year-old Dutchman, who has played once for the Netherlands, agreed on a four-year deal estimated at eight million pounds last month but if Norwich fail to maintain their top flight status, the move could fall through.
Norwich are 14th in the table but are just just four points above the relegation zone with five matches to play.
Van Wolfswinkel's representative Louis Laros told A Bola newspaper in Portugal: "There is a special clause in the deal accepted by all parties that stipulates if Norwich leave the Premier League then the future of Ricky van Wolfswinkel will be open again.
"That is the reality, but we are confident in the ability of the English club to remain in the top division.
"For now, Ricky is only thinking about Sporting and helping them to get results. At the end of the season, he will start to focus on Norwich."
The player, nicknamed "O Lobo" (The Wolf) in Portugal, has scored 26 league goals for Sporting in 50 appearances after previously playing for Vitesse Arnhem and Utrecht in the Netherlands.