Defoe has struggled for game time at Bournemouth, though the 35-year-old scored a last-gasp equaliser in Saturday's 2-2 draw at Watford in the Premier League.
The 57-cap international has not started a Premier League match since December and while he admitted the situation is frustrating, Defoe is confident he can make an impact for England if called upon by manager Gareth Southgate.
"I would come on and win the World Cup, it's as simple as that," Defoe said.
"You come on for one minute, two minutes, and if there's a chance you score. At a tournament, it is not just about the players who start, it's about the squad. It has been a stop-start season for me but I can't sulk."
"No-one wants to sit on the bench," Defoe added. "If you get to the point where you accept sitting on the bench then you shouldn't be playing. I know there are still a lot more goals in me.
"I came here [in the summer] as an England player. I worked so hard to get back in that squad.
"I have missed the last three squads because I am not playing. I spoke to the manager a few months ago and it's as simple as that — you have got to be playing and scoring goals.
"I understand I have got to be playing. You can't just assume you are going to get in the squad because of what you have done over the years."