Ms Sturgeon refused to rule out the prospect at First Minister’s questions after former SNP deputy leader Jim Sillars said the party should propose another vote “when it suits us” in its 2016 manifesto for re-election.
The First Minister accused her opponents of “desperation”. Last year she described the referendum as a “once in a generation” event.
Mr Sillars – deputy leader of the party in the mid-1990s – said: “I can’t see a membership of 100,000 which came in on the independence issue not demanding that in the manifesto.
“It would be astonishing if you joined the SNP because you desire independence as soon as you can possibly get it and not expect it to be in the manifesto.”
Mr Sillars, husband of the late SNP trailblazer Margo MacDonald, was a high-profile campaigner for the Yes camp.
He added: “I cannot believe that there will not be a commitment to independence and a referendum in an SNP manifesto next year, with the timing of the referendum to be left to a decision when we think the time is right.
“Now, that could be within a short period or within two or three years, one doesn’t know.
“The important thing is that next time there is a referendum we pick the time when we are going to win.”
Opposition MSPs at Holyrood called on Ms Sturgeon to rule out the move.
Liberal Democrat leader Willie Rennie said: “She could make a statement right here, right now that in the next term of this parliament there will not be another referendum – why can’t she just say that?”
He added: “This is the neverendum that we warned about. We saw the consequences of the whole machinery of government being focused on the referendum for the last three years.
“The NHS and the police bear witness to that problem, and in Quebec we have seen the long period of political uncertainty and the economic consequences of that.” Labour’s deputy leader Kezia Dugdale pointed to a string of Nationalist candidates who have suggested that another constitutional vote could be on the cards.
Ms Sturgeon said that unless there is a “change in the circumstances” from the last referendum, there will be no proposals for another. But she added: “If the SNP ever does propose in a manifesto a second referendum that, in and of itself, does not bring about a referendum.
“People in Scotland first have to vote for that manifesto and give the SNP sufficient numbers in this parliament to get the legislation through – that’s democracy.” She added: “I’ve got the greatest of respect for Jim Sillars, but the clue is in his title, former deputy leader of the SNP.
“I’m the current leader of the SNP. So let me say it clearly once again: this election is not about independence, it’s not about a referendum. It’s about making Scotland’s voice heard.”
Meanwhile, the Conservatives confirmed David Cameron would not block another referendum if he remains prime minister and if the SNP secure a mandate next year.
Scottish Conservative leader Ruth Davidson told MSPs she has discussed the approach to another referendum “at length” with Mr Cameron.
Ms Davidson said the Edinburgh Agreement, which delivered Westminster’s consent for the 2014 poll, established the terms for future votes.
“There is an absolute precedent and I do not deviate from that precedent,” she added.
When asked whether she would advise Mr Cameron to block another referendum, she said: “Absolutely not. We have and have always believed in self-determination and democracy.”
Labour in Scotland launched a new poster yesterday which it claims underlines “Scotland’s choice” in the General Election between a fairer economy with Jim Murphy’s party or another “divisive referendum” with the SNP.