A second independence referendum is "unlikely" to happen within Nicola Sturgeon's preferred time frame, a former SNP senior staff member said.
Kevin Pringle also warned that, if a vote on leaving the UK is held before the end of 2023, the SNP's goal of increasing support for independence may be "undermined".
The First Minister has repeatedly said her intention is to hold indyref2 by the midway point in this Holyrood term - although the UK Government remains hostile to such plans.
Pringle, who worked as a special adviser to Alex Salmond when he was first minister and also worked for the Yes Scotland pro-independence campaign, said it is "unlikely" there will be a fresh vote on the issue by the end of next year "given the hurdles to be overcome".
Writing in the Sunday Times, he said: "It is unwise to make any definite predictions in such volatile times, but it seems reasonable to say out loud that an independence referendum is unlikely to take place by the end of next year, given the hurdles to be overcome and extensive preparations required.
"I don't think the war in Ukraine has changed this, in the sense that it was no more likely before the Russian invasion and all the destruction and instability being wreaked."
"A referendum is a means to an end, nothing more. If the Scottish government pursues it within a tight 2023 timescale that people are uncomfortable with, even assuming it doesn't happen then, the task of building support for independence itself may be undermined."
Pringle said the "mandate" SNP and Green MSPs - who also support the holding of a second referendum - were elected on in last May's Holyrood elections was to hold a referendum in the current five-year Scottish Parliament term.
With four years still to go, he added: "That provides time enough to get it right."
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