The 24-year-old striker, who agreed an £8.5m move from Portugal last month, scored an impressive hat-trick at Braga on Monday night.
"Of course it is hard to explain to people - some people think I am already in England," he said. "But I'm here in Sporting and I think I showed tonight that I want the best for Sporting and for the team, and it's no reason for me to keep calm and play easy. I need to give my maximum for Sporting. They deserve that.
"It is always sad when you leave a club that you really like. But it is also a new step for me in my career, to play in the Premier League and to develop myself.
"But the season is not finished yet so I don't want to think too much about England. I want to focus on Sporting now and these are the only three points I can think about now."