Richard Leonard has said there is growing evidence Labour will "almost certainly" vote against the final Brexit deal.
The Scottish Labour leader said it was becoming more and more difficult to see how the party could back any deal the UK Government secures on leaving the EU.
Mr Leonard also said he was open minded about the possibility of an internal referendum on the party's Brexit position as well as a bespoke migration policy for Scotland.
At an event hosted by the David Hume Institute in Edinburgh, Mr Leonard repeated his belief that an early general election is more likely than a second referendum on EU membership.
Of the negotiations, he said: "We are starting to get into areas where it becomes more and more difficult to see how that would sustain the kind of jobs-first, economy-first approach that Labour is taking.
"So I can certainly see there being growing evidence that we will almost certainly vote down the deal when it comes back to the UK Parliament.
"I can see that precipitating a major constitutional crisis, I can see there being growing pressure, even amongst the ranks of the Conservative MPs, there will be growing pressure to find an alternate way of resolving this and I think one of the ways they may seek to resolve it is by being forced, or volunteering actually in the end, to call a general election."
Asked about the possibility of an internal party referendum on Brexit, he said: "There are routes through which affiliated organisations, Labour Party members can promote that debate inside the Labour Party.
"So I don't think there is any closure on that, I think it's perfectly feasible for there to be a consideration of Lord Adonis' proposal within the framework of decision making inside the Labour Party.
"I'm in favour of Labour Party internal democracy and nothing in my view would be ruled out if somebody wanted to raise that to change or to revise Labour Party policy, but they would need to attract a majority view."
Mr Leonard also said he was open minded about the possibility of bespoke migration positions across the UK post-Brexit.
He said: "I am somebody who is very open to persuasion on there being a nuanced policy.
"I'm quite open minded about the question of whether there should be a variation on migration policy in Scotland and I think it's something which we need to discuss."
But he warned about such a debate being used as a tool for companies to bring in labour at a reduced rate.