Mexico striker Castillo is expected to seal a year-long loan deal next month from Shakhtar Donetsk.
The Italian forward has now found the target in his last two matches and insists he is happy at the club.
The 23 year old told the Manchester Evening News: "I do not want to leave, I see a future for me here.
"Getting into the side and staying there is a challenge for me and I want to win that challenge.
"It was important for my confidence that I was able to come on at Spurs and score and then start the game against Bolton.
"Now I hope that goal will be the start of many. I have worked hard and aim to make the most of my chance."