During PMQs, Sir Vince Cable asked Mrs May to confirm that in her conversations with Mr Trump she had made it "absolutely clear" the "NHS is not for sale".
May was pressed by Liberal Democrat leader Vince Cable over whether she would allow a future trade deal to give United States corporations the right to bid on lucrative NHS contracts.
Under the European Union's Transatlantic Trade and Investment Partnership with the USA, the EU had negotiated assurances that nations would be free to control their own health services and avoid forced privatisation and legal actions that would make reversing health service sell offs nearly impossible.
However, both the White House and British government said their discussion did not touch on the USA president's remarks on the NHS, focusing instead on more pressing matters.
The spokesman added: "Any trade deal ensures decisions about public services continue to be made by United Kingdom governments, not by our trade partners".
Theresa May has come under fire for failing to guarantee that the U.S. will be able to access NHS contracts as part of a future trade deal.
The Prime Minister was asked in the Commons if she could give an "absolute guarantee" the health service would not be on the table in future trade negotiations with Washington.
During Prime Minister's Questions (PMQs) in the Commons on Wednesday, the Tory leader was quizzed on the exact terms of any post-Brexit trade deal between the United Kingdom and US President Donald Trump's administration.
"We are starting discussions with the American administration, first of all looking at what we can do to increase trade between the U.S. and the United Kingdom already and before the possibility of any free-trade agreement and he (Vince Cable) doesn't know what they're going to say in their requirements for that free-trade agreement".
The row comes within days of the U.S. president criticising the NHS.
Shadow health secretary Jonathan Ashworth said: "Our NHS should never be up for sale".
"Critics say this rising "privatisation" has opened the door to U.S. health firms, who already view the NHS as a goldmine", adds the paper.
President Donald Trump spoke with British Prime Minister Theresa May on Tuesday, a day after the US leader attacked the U.K.'s health care system.
'Clearly the British public can't trust our public health service with a flip-flopping Prime Minister and a party that has spent nearly eight years running it down'.
"Theresa May's comments today exposed the Tories" shaky commitment to our NHS in the quest to cosy up to Donald Trump.