Donald Trump made the comments ahead of a meeting with the British Prime Minister at the G7 summit in France.
Donald Trump says the US and UK will discuss doing a "very big trade deal."
Negotiations are expected to be turbulent as the first full day of discussions goes ahead.
Boris Johnson is due to meet the European Council president this afternoon where the Prime Minister is expected to tell EU boss Donald Tusk that Britain will only pay a quarter of its so-called Brexit divorce bill if the country leaves without a deal on 31 October.
It is understood he will tell Mr Tusk that under no deal, the UK would only owe about £9bn of the £39bn liability agreed by former Prime Minister Theresa May.
The approach is likely to raise tension with other EU leaders at the meeting in Biarritz.
In June, a source close to French President Emmanuel Macron, who is hosting the G7 summit, said refusing to pay was the "equivalent to a sovereign debt default".
Others argue the UK is legally bound to pay the £39bn sum and warn that reneging on the obligation will prevent a future trade deal being struck and could even lead to the EU pursuing the funds through the courts.
It follows a war of words between Mr Johnson and Mr Tusk on Saturday over who would be to blame if the UK left the EU without an agreement.
Additional reporting: IRN.