Lib Dem home affairs spokesman Nick Clegg has said he would probably stand for the party leadership in the future.
Mr Clegg urged the party to 'hold its nerve'
When asked at a fringe meeting to state his future intentions, Mr Clegg said "if you are asking me would I stand against Ming, the answer is no".
When pushed on the issue, he responded that "if there was a vacancy in the future then I probably would".
It comes as a Guardian/ICM opinion poll suggests Sir Menzies Campbell is now more popular than David Cameron.
The findings will be seen as a boost for the Lib Dem leader, who has faced continued questions about his performance during this week's conference.
Speaking at a fringe event in Brighton, Mr Clegg urged the party to support Sir Menzies and "put two fingers up" at its critics.
The Sheffield Hallam MP, who along with environment spokesman Chris Huhne is most often tipped as a future Lib Dem leader, said: "You have to sometimes hold your nerve.
"At a time when Sir Ming is being attacked with barely disguised ageism... the only response is to pull together, put up two fingers and say, don't you dare push us around."
He refused to answer questions about entering into a potential coalition with either the Conservative or Labour parties following a general election.
"It would be idiotic and illogical to rule out coalition, but the point is that pluralism in British politics does not yet occur," Mr Clegg said.
The Guardian/ICM poll gives Sir Menzies a narrow advantage over Mr Cameron.
Some 36% of those taking part said they were satisfied with Sir Menzies and 41% dissatisfied - a net rating of minus five.
The survey suggests 37% of all voters are satisfied with the way Mr Cameron is doing his job, against 45% who are dissatisfied - a net satisfaction rating of minus eight.
By contrast, Prime Minster Gordon Brown enjoyed a comfortable satisfaction rating of plus 32, with 55% of all voters saying they are happy with the way he has performed since his arrival in 10 Downing Street in June, against 23% who say they are not.
The poll puts Labour support in a possible general election at 40% - up one point on a similar survey last month - with the Conservatives down two on 32% and the Lib Dems up two on 20%.
ICM questioned 1,005 adults by telephone between 13 and 16 September.
Lib Dem campaigns chief Ed Davey said the poll showed the party's message on the "environment and fairness" was getting through.
"The more coverage we get, the more people see of our ideas and our policies, the higher our poll rating goes. The reverse seems to happen with Tory leaders" Mr Davey told reporters.
Asked whether he had leadership ambitions of his own, he said "there is no vacancy".
Chris Huhne has said it would be "premature" for him or any other frontbenchers to discuss who might replace Sir Menzies.
Mr Huhne told the BBC: "There is no vacancy and it would be premature to even talk about the possibility as there is no vacancy.
"I am not a sort of Michael Heseltine figure who plans their route map to Downing Street from the day they come out of nappies. I wait for opportunities and decide at the time.
"I am very glad to be doing the environment brief which I think is the key challenge facing the country."