The Netherlands international revealed he left Estadio Jose Avalade because of their constrained financial situation, managerial instability and the lure of the Premier League
The Dutchman agreed to join Chris Hughton's side earlier this year and felt the need to defend what he believes many people percieve is a move to a lesser club.
The 24-year-old says he has been keeping a watchful eye on the Canaries, while their manager has given him every confidence he will given a chance to shine at Carrow Road.
"Some people may see my transfer as a step back. But the Premier League is bigger than the Portuguese league," he told reporters.
"Life is good in Portugal, but the football has to be on a certain level too. Sporting ended this season as seventh in the league. The club has not won prizes for many years. Sporting remains a big club, but especially because of its history.
"Norwich is a small club compared to Sporting, but also a friendly club with a beautiful stadium and good fans. That suits me. The manager said I will be his number one striker. I know I have to battle for it, but it's always good to get the confidence."
The striker said he left Sporting Lisbon because of their dire financial situation and the lack of managerial stability at the club, meaning players and staff often went unpaid.
He continued: "Sporting needed money. They have to take a step back and they are choosing for youth players.
"For months I did not received any salary. People say that players earn enough money, but it's still our salary. It was a strange and weird situation. You also talk about people from for example the medical staff. They have to pay their mortgage.
"Players can manage a bit longer without salary. I had five coaches in two years. That says something."