The 24-year-old Dutchman, who has played once for the Netherlands, agreed on a four-year deal estimated at £8million last month but Van Wolfswinkel's representative Louis Laros claimed if Norwich fail to maintain their top flight status, the move could fall through.
Norwich are 14th in the table but are just four points above the relegation zone with five matches to play.
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."
Hughton, however, slammed the door shut on that possibility this afternoon as he prepared for Saturday's vital home clash against rock-bottom Reading.
He said: "I have heard those reports but the facts are that he has signed for Norwich City and I expect to see him on the first of July.
"Any talk of a relegation clause in the contract is not fact. That is where we are and we look forward to seeing him next season."
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.
- Sports & Recreation
- Van Wolfswinkel