Defoe, 30, has been in excellent form in the Capital One Cup and Europa League this term with seven goals already to his name.
However, big summer signing Roberto Soldado has emerged as first choice under Andre Villas-Boas and Defoe has yet to start a league game this season.
And Defoe admits that he is worried that his England place could come under pressure ahead of next summer's World Cup in Brazil.
"It is great to score in those competitions but I feel you have got to be scoring in the Premier League," said Defoe.
"I don't think at my age I have got anything to prove but to get into the squad that goes to a major tournament, you have got to be playing for your club.
"As you can imagine, it is very frustrating - especially after I worked so hard pre-season and telling people 'I feel sharper and stronger than ever.' That has shown in my games.
"I don't know what more I could do really. I am doing my talking on the pitch.
"Scoring goals is the answer, going out there and showing the manager what I can do.
"Obviously you have a word with the manager. I speak to Andre and stuff like that. But I have got to play, it's a World Cup year."