David Davis has said he is not certain the UK will secure a withdrawal deal with the EU.
The Brexit Secretary's comments come after Chancellor Philip Hammond said that no deal would be "very, very bad" for the UK.
While Mr Davis said he was "pretty sure" an agreement could be struck, he left the door open to leaving the bloc without one.
Asked if he was sure there would be a deal cut, Mr Davis told the BBC's Andrew Marr Show: "I'm pretty sure, I am not 100% sure, you can never be, it's a negotiation.
Mr Davis said it was part of his role to plan for a bad outcome.
He said: "Half my job is the invisible job of actually planning for all outcomes, the good, the bad, the whole range."
Asked if he agreed with the Chancellor that no deal would be very, very bad, Mr Davis said: "It would be better than a punishment deal.
"'I'm being very clear about this. In my job I don't think out loud, I don't make guesses. I try to make decisions, you make those based on the data."
Mr Davis said Britain would need transitional trade arrangements with the EU for a time after Brexit.
He said: "We think that there will be a transitional period, not that long. I think one to two years is more likely. It will vary. This is something incredibly practical."
Labour's shadow Brexit secretary Sir Keir Starmer said it would be a disaster to fail to secure a full withdrawal agreement with Europe.
"Labour has been clear that no deal is not a viable option as it would be catastrophic for British trade, jobs and security. The sooner David Davis realises this, the better," he said.
"Instead of preparing for failure the Government should be putting all their efforts into getting a Brexit deal that works for Britain - that means putting jobs and the economy first and dropping the no deal mantra."