The two leaders will hold talks at the Prime Minister's country residence of Chequers where Russia, Brexit and the Middle East will top the agenda.
The giant inflatable "Baby Trump" balloon will be flown near the Houses of Parliament ahead of the protest.
Sadiq Khan supported the decision taken by the Greater London Authority to allow the 20ft inflatable, dubbed "Trump Baby" to rise above Parliament Square Gardens for two hours on Friday morning while the U.S. president is in London.
He has clashed in the past with May - even though she is a fellow conservative who shares his view that defense spending should be hiked - and with her predecessor, David Cameron, who challenged Trump's anti-Muslim campaign stance as "divisive, stupid and wrong".
"I like Boris Johnson, I've always liked him", said Mr Trump. He said it was an example of why universal healthcare should not reach United States shores. "It seems so un-American". They have already ordered sufficient helium to pick up en route to power the weekend's activities.
While tens of thousands of Brits are set to protest Donald Trump's visit on Thursday, one pub in west London will be welcoming him with open arms.
The U.S. Embassy in London released an alert on Tuesday urging Americans to "keep a low profile" during President TrumpDonald John TrumpMcConnell to meet with Trump's Supreme Court pick Tuesday Kavanaugh offers lengthy judicial record ahead of bitter confirmation fight Hundreds protest Kavanaugh's nomination outside Supreme Court MORE's scheduled visit to the United Kingdom later this week.
On knife crime: The president claimed a hospital in the capital had "blood all over the floors" amid a wave of knife crime, adding: "They say it's as bad as a military war zone hospital".
Mr Trump's mother, the late Mary MacLeod Trump, was Scottish. We believe that this publicly-owned facility should not be used for Donald Trump's visit.
"From the public, the welcome will be far from warm", he told lawmakers on Wednesday. It was an extraordinary rebuke from a close ally.
"There is no stronger alliance than that of our special relationship with the USA and there will be no alliance more important in the years ahead", May said in a statement.
The security operation is estimated to cost between £8m and £10m and will put police under "unquestionable pressure", according to Police Federation chairman Simon Kempton, who said operations were likely to become "merely reactive" during the visit.
A Facebook event called "Trump not welcome - make noise as he arrives" plans to protest right outside where the president will be staying - the US Ambassador's residence in Regent's Park - when he checks in on the evening of Jul 12.