Clarke: not for turning on the euro
Mr Clarke, who lost out to Mr Duncan Smith in the battle to lead the party, has previously said he would not join the frontbench unless he could have the top job.
But in an interview with the epolitix website, Mr Clarke hinted that he might now accept a front bench role if Mr Duncan Smith offered him one.
"It depends what job and it depends what he expects me to say about the policy of the party," Mr Clarke said. "Never say never in politics."
Euro 'mistake'
However, the pro-euro former chancellor sharply criticised Mr Duncan Smith's uncompromising stance on the single currency.
"But I'm not wanting to go on the front bench and I'm perfectly absorbed in politics doing what I'm doing as a backbencher," he added.
Mr Clarke said the Conservatives would not find any stability until a referendum on the euro had decided the issue "one way or another".
Former leader William Hague's "extraordinary" Save the Pound campaign was the reason why the Conservatives lost so heavily in the general election, he went on.
"We would have lost anyway but no doubt it was made worse," Mr Clarke said.
Leadership result
Describing how he felt when he found out he had lost the Tory leadership contest, Mr Clarke said he was "disappointed", but not "totally surprised."
"Most of the (Tory leadership) electorate were elderly people who pay their subscription and never attend meetings and sent in a postal ballot after reading the Daily Telegraph.
"It was quite hard work getting their votes."
Commenting on reports of a rift between Tony Blair and Gordon Brown, Mr Clarke said tension between prime ministers and their chancellors was inevitable.
On his relationship with John Major, Mr Clarke said: "At times we irritated each other quite a bit - we were bound to," but, he added, they had remained friends throughout their period in office.