Echoing remarks made by Washington's ambassador to London, the president said any future transatlantic talks must mean "everything" being discussed.
Asked at a press conference - alongside Theresa May at the Foreign Office - whether the whole economy, including the NHS, should be part of negotiations, he replied: "Look, I think everything with a trade deal is on the table.
"When you're dealing in trade everything is on the table. So NHS or anything else, a lot more than that, but everything will be on the table, absolutely."
But the prime minister attempted to downplay Mr Trump's remarks on the second day of his official UK state visit, claiming: "The point about making trade deals of course is that both sides negotiate and come to an agreement about what should or should not be in that trade deal for the future."
Matt Hancock, the health secretary vying to replace Ms May as prime minister, immediately hit back on social media making clear any future trade deal brokered between the UK and US will not include the NHS.
"Dear Mr President. The NHS isn't on the table in trade talks - and never will be. Not on my watch," he said.
The British Medical Association (BMA) also issued a statement, urging all the contenders in the Tory leadership race to commit to excluding the NHS from any post-Brexit talks.
The organisation said: "We have an unequivocal message for the next Conservative leader and the future prime minister: profit should never take priority over the protection of the health service and the healthcare of citizens."
Speaking just days before Mr Trump, the US ambassador to the UK, Woody Johnson, told the BBC's Andrew Marr Show: "I think probably the entire economy, in a trade deal all things that are trade will be on the table."
Mr Johnson also said chlorinated chicken - which is permitted under American regulations but banned in the EU - was "completely safe".
He added: "Once again, you can have a choice. We have five million Brits, British people, coming over to the US every year and I’ve never heard a complaint, one complaint about anything to do with chicken."
Responding to Mr Trump's remarks, Jonathan Ashworth, the shadow health secretary, said US corporations taking over the NHS "is a nightmare scenario".
He continued: "The Tories appear happy to give Trump what he wants, and some want to offer up our NHS to get the No Deal Brexit they are campaigning for.
"If our NHS is taken over by US corporations, it will undermine it as a free, universal public service. The NHS is only safe in Labour hands."
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