Defoe admits it is frustrating having to keep proving himself but will never sulk and will strive to take every opportunity that comes his way.
He said: "It is frustrating but all you can do as a player is make sure you are still around, still in the squad.
"I've always said once you get a chance, you've got to take it and after that you leave it down to the manager. I'll go back to my club and hopefully get off to a good start to the season and leave it down to the manager.
"What I would say is every time I get called up for England, if I'm fit I'll be ready and will always give it my all."
He added: "I'm not one of those players that will sulk or anything like that (if not playing).
"I just keep it going because, if you sulk and then do get a chance, because your head has gone you can't really perform. I've never been a sulker. I've always waited for my chance and when I get one, make sure I grab it with both hands."