Slimani turned down West Ham
The Algeria international reportedly caught the eye of manager Sam Allardyce with his performances at the World Cup, where he scored two goals in four appearances.
And Slimani, who concedes he would one day like to play in England or Germany, now says he was in advanced talks with the Upton Park club over a move, but is happy with his decision to remain in Portugal.
"Yes [there were negotiations], but thank god I stayed with Sporting," he told Le Buteur. "I made the right choice. Stability is a positive.
"I have to work to make more progress, and then I can think about moving elsewhere."
Slimani is part of the Algeria squad at the Africa Cup of Nations.