"This was, without doubt, the lowest point of my career. I'm devastated," he told the Sun.
"I can't remember much of the conversation. As soon as he told me I was not in the squad I switched off. I was heartbroken.
"I got left out of the squad in 2006 by Sven-Goran Eriksson after travelling to the training camp and never wanted to feel that low again. This feels far worse than then."
Defoe, who has 19 goals for England, swapped the Premier League for the MLS in February but does not believe that is the reason for his omission.
"Some people are talking like I've been here for four years rather than two months," he added.
"I never had a discussion with Roy about any possible impact on my England chances coming here because I didn't feel the need to. And I did read a quote from him, saying that me playing in MLS doesn't change anything because he knows me as a player."