"I can't see how it can be avoided, frankly," Jim Sillars said when asked about the possibility of the SNP promising another independence vote next year.
The politician added that tens of thousands of the party's new members are seeking a commitment to another referendum from the party leadership.
"I can't see a membership of 100,000 which came in on the independence issue not demanding that in the manifesto," Sillars said.
The SNP, which is the majority party in the current Scottish Parliament, campaigned for Scotland to break away from the United Kingdom ahead of the 2014 independence vote.
The party first promised to hold a referendum in the run-up to the 2007 Scottish Parliament election, which the party went on to win.
The SNP reiterated their pledge during the following election campaign in 2011 before securing a majority of seats in the Parliament.
The referendum was held in September 2014, but just over 55 percent of the voters rejected Scotland becoming be an independent state.