The Derby County manager took charge of the Three Lions in August 2006, but was sacked the following November after his side's failure to qualify for Euro 2008.
McClaren believes that he let the country down and claims that he is still disappointed at not being able to take them to a major tournament.
"At the time I thought I was ready, but the job finds out that you're not ready," The Mirror quotes him as saying. "I didn't have the experience and, together with a little bit of bad luck as well along the way, it didn't work out.
"The biggest thing that hurt me that night, and ever since, was the failure to qualify. That is the biggest thing. It was nothing about anything else. As I said on the night, it felt like I'd let the nation down.
"That's what I've had to live with. That's the hardest thing. Nothing else – like 'The wally with the brolly.' The disappointment will not go away and that still hurts, but you have to get on with life and football."
McClaren's current club Derby will be hoping to book their return to the Premier League when they take on Queens Park Rangers in the Championship playoff final on Saturday.