The 21-year-old midfielder has been restricted to just 18 appearances in four years at White Hart Lane, with eight loan spells taken in during that time.
Townsend told the Evening Standard: "Ever since I was 17, I've been told I'm unlucky because I have two of the best wingers in the world, Gareth Bale and Aaron Lennon, ahead of me. But I'm 21 now. I'm not a youngster any more.
"I understand what people mean but I can't just sit in the reserves and say, 'Look who's ahead of me'. Andre Villas-Boas has said it to me, too, so I hear it a lot.
"You can do well in the lower leagues but the manager will always wonder if you can do it at the top level. Look at Steven Caulker, he did brilliantly for Swansea last season and now he's played regularly for Spurs and he's played for England.
"This is my big chance to show the people at Tottenham what I can do, playing on the stage they're on. Andre Villas-Boas has told me he doesn't want to sell me and that I'm in his plans for the future.