The physician behind a heavily-criticized assessment of Donald Trump's health composed it in just five minutes while a limousine sent by the presidential candidate waited outside, NBC News reported.

"I think I picked up his kind of language and then just interpreted it to my own," Harold Bornstein said of the note, in which he said that Trump would be the "healthiest" person ever elected if he defeats Democrat Hillary Clinton in November.

Bornstein has been publicly questioned by CNN medical correspondent Sanjay Gupta, who chided him for saying that Trump scored "positive" results on his purported medical exams. Trump released the letter last December instead of providing medical records.

Gupta also suggested that Bornstein exaggerated his credentials, saying he was a "fellow" for the American College of Gastroenterology -- when in fact he has not been a member of the organization since 1995 -- and also misleadingly said that he had admitting privileges at Lenox Hill Hospital in New York City.

But Bornstein defended his assessment of Trump on Friday, saying that "his health is excellent, especially his mental health."