"I can't play at Spurs, that's for definite," Defoe told talkSPORT.
"I wasn't sure but that's how it is and I'm gutted. But you look at the situation and you say 'I definitely made the right move'. It's important to play football and more importantly to play with good players.
"I feel sharper than ever, I feel fitter than ever and I could keep running all day."
Defoe also believes he is being denied what would have been a warm reception from his fans in north London.
"I've bumped into a few Spurs fans and they said 'we were really looking forward to you coming back, you're going to get a great reception'."
Defoe was rewarded for his recent exploits in front of goal with a place in Fabio Capello's second England squad, something he rates as one of his priorities after struggling to become a regular during his time at Tottenham.
"I'm quite proud of myself," he said.
"When I was at Spurs I had a hard time, I had some good times there too but it was difficult. Coming to Portsmouth could not have gone any better.
"Going away with England feeling good about yourself is important; you look forward to meeting up with the boys.
"I believe if I do what I'm doing at club level I'll get the opportunity (with England). Then I've got to try and keep the shirt."