Trump said on Monday the agreement by which the United Kingdom will leave the European Union may make trade between Washington and London more hard - handing ammunition to May's critics at home who want to block the Brexit deal.
British Prime Minister Theresa May will travel to Northern Ireland and Wales as part of a tour of the United Kingdom created to rally support for her widely criticised Brexit deal before a vote in parliament.
"That wouldn't be a good thing".
"The failure of the pound to rally on recent positive developments suggests the market is pricing in that the deal won't pass the first time in parliament", said Lee Hardman, a currency analyst at MUFG.
"We have already been laying the groundwork for an ambitious agreement with the USA through our joint working groups, which have met five times so far", the spokeswoman said.
"We have already been laying the groundwork for an ambitious agreement with the United States through our joint working groups, which have met five times so far", it added.
Mr Varadkar said: "There isn't a plan B. What's being put in front of European Union parliament and House of Commons is a deal".
Mr Trump's intervention came as it was confirmed that MPs will vote on Mrs May's Brexit deal on December 11 after five days of debate.
But she is embarking on a PR blitz this week as she tries to convince the public to back her Brexit deal and put pressure on MPs to support it as it goes to a vote in Parliament.
But despite May constantly stating that "no deal is better than a bad deal", a no deal scenario would have cost Britain around £140 billion a year and led to a 5% fall in GDP, the report said.
The vote in parliament is scheduled for December 11.
She is facing widespread scepticism from within her own Conservative party and more broadly about the terms of an agreement.
May returns to a mutinous parliament after sealing the agreement with European Union leaders at a summit in Brussels, where both sides insisted the divorce deal was the best and only option available.
"The message I have clearly heard here today from across the board - from the voluntary sector, from young people, from businesses, from the cultural sector, from academics - is the importance of that certainty and the importance of Parliament accepting that deal so we can move on to develop our future", she said.
Spanish Prime Minister Pedro Sanchez said on Thursday: "After my conversation with Theresa May, our positions remain far away", adding: "If there are no changes, we will veto Brexit".
"The idea she is trying to push - that her deal is effectively "take it or leave it" - is frankly baloney".
In a riposte to French President Emmanuel Macron's suggestion that the EU could delay trade talks unless its fishermen were granted access to United Kingdom waters, the PM said: "The EU have maintained throughout this process that they wanted to link overall access to markets to access fisheries".
In a letter to the nation issued by 10 Downing Street this weekend, May once again pleaded with the public to get behind her deal which will mark "a new chapter in our national life".
Forged during 17 months of tough negotiations, the withdrawal agreement covers financial matters, citizens' rights, Northern Ireland and arrangements for a 21-month post-Brexit transition phase.