The 31-year old Croatia international has admitted he was aware of interest from the Toffees in January and was hoping they would again come for him this summer.
"David Moyes publicly announced that he wanted me at Everton, " Pranjic told Sportske Novosti.
"But then I got a feeling that things were moving too slow and I didn't want to wait anymore.
"I could have waited until the end of August but then Sporting knocked on my door and I knew right away that this is what I want.
"I could also have gone to Besiktas but Sporting was such a good option for me that I couldn't say no."