His comments come as France joined Germany in challenging the Prime Minister to come up with a backstop alternative within 30 days.
He said: "They could see that we want a deal, they can see the problems with the backstop. Clearly Angela Merkel thinks that the solutions can be found within 30 days - actually what she meant was if you can do it in two years you can certainly do it in 30 days.
"But I want to caution everybody, OK? Because this is not going to be a cinch, this is not going to be easy. We will have to work very hard to get this thing done."
He continued: "We have to have an arrangement that allows the whole UK to come out of the EU and have frictionless trade at the border in Northern Ireland.
"There are lots of ways that we can make sure that happens.
"But to persuade our EU friends and partners, who are very, very, very hard over against it, will take some time.
"I'm afraid we will have to prepare to come out without an agreement and we can do that, we are very confident that we will be OK because we will have all sorts of preparations in place."
He added: "We are making progress but I am just telling people not to hold their breath, because I have seen the way these Brussels negotiations work."
It was "always on the steps of the court, as it were, that the deal is done", he said, and "I must urge people - we are going to be working very hard on this but they shouldn't necessarily get their hopes up too soon".