President Trump said Thursday he will be “surprised” if his upcoming physical produces negative news about his overall health, saying the stock market could tank if he's wrong.

Trump's routine doctor’s visit is set to occur Friday and comes amid heightened speculation about his fitness for office. Comments contained in a new tell-all book about his presidency have led several critics of the current administration to question his mental health.

But the president told reporters he expects Friday's exam to go smoothly.

“I think it's going to go very well," he said during a round table in prison reform, noting that he would be “surprised if it doesn't.”

"It better go well, otherwise the stock market will not be happy," Trump added.

The White House has promised to provide a detailed readout of the exam next week, when Trump's doctor briefs reporters on the results.