President Donald Trump hinted that he wanted to see President Joe Biden's medical doctor be investigated after the former president's shock cancer diagnosis.

In the Oval Office on Monday, Trump was asked to react to Biden's diagnosis and was asked if he planned to call his predecesor.

Trump responded by calling the news 'very sad' but then segued and suggested that there might have been a cover-up, as others on the political right have floated.

'I'm surprised that it wasn't, you know, the public wasn't notified a long time ago because to get to stage nine, that's a long time,' Trump said.

After boasting about acing his own physical - and noting that he had taken a cognitive test - he suggested something was awry with Biden's White House doctor.