Castellazzi will be between the posts at White Hart Lane with current No1 Julio Cesar out injured.
"I have played so many and in all the Divisions that it's difficult to say so," he smiled when asked if the Spurs game was the biggest of his career.
"But making your debut as a starter in the Champions League, in an English stadium, defending the European champions' goal, doesn't happen every day.
"It seems like it was written by a screenwriter. It seems like a film. Julio Cesar is injured and Gomes is suspended.
"Finding each other again in Tottenham's match against Inter is the right reward for rising up through the ranks."