The 66-times capped flanker was on Sunday omitted by head coach Sir Clive Woodward, together with fellow World Cup winners Kyran Bracken and Martin Corry.
The Leicester player had no inkling he was set to be dropped, with Woodward maintaining his decision was always to pick a squad on the current form.
"I was shocked," said the 35-year-old. "A couple of months ago I was a world champion.
"I was on top of my game then and nothing has changed from my personal view. I don't think my form has dipped since then, but Clive picks the team."
He added: "My kit had been laid out at home ready for me to drive down to the team hotel in the morning.
"I've spoken to Clive and he didn't want to take me down there just to send me back because he didn't need me in the 22."
Back, though, has not ruled out an international return.
He declared: "My motivation to play the game of rugby and my enthusiasm hasn't dipped.
"As long as I'm playing rugby union at club level, I will aspire to get into the England team."