"There are a number of reasons why I've been thinking about this," Carragher, 29, told the Liverpool Echo. "I first thought about it after the World Cup as I wondered how many chances I would get at centre-half."
"Given my form for Liverpool, I genuinely thought that was possible but over the last 12 months, players like Jonathan Woodgate and Ledley King have played there ahead of me."
Carragher played at full-back in the friendly against Brazil on 1 June when England drew 1-1 in the first game at Wembley since the stadium's facelift.
He was then expected to figure in manager Steve McClaren's plans against Estonia but his omission seems to have had a major bearing on his thinking.
"It was particularly disappointing for me when Rio was out against Estonia and I wasn't picked," said Carragher. "I thought I'd had a good season for Liverpool, especially helping Liverpool get to the Champions League final.
"Like any player I thought I deserved to play but not doing so made the situation crystal clear to me."
Carragher says he wants to step aside to give younger players like Everton's Joleon Lescott and Steven Taylor of Newcastle a chance. But he will make himself available if England have an "absolute emergency" as they head toward the climax of their Euro 2008 qualifying campaign.
"I want to stress this has nothing do would Steve McClaren," added Carragher. "It wouldn't have mattered who was the England manager, I've been thinking about this for a while.
"I've worked with Steve for five years as part of the England set-up.
"I have a great time working with him and a lot of the England coaches. I'm just thinking about this from a purely personal point of view.
"The reason I'm delaying a final decision is because I didn't want people to think I have a bad attitude or I'm turning my back on the country at a bad time."