An expert Thursday warned that President Donald Trump's health has started to rapidly deteriorate as questions increase over his mental capacity and ability to lead, according to reports.

Dr. John Gartner, psychologist, psychiatrist, and a former assistant professor at John Hopkins Medical School, told British publication The i Paper that there have been increased concerns over the president's health and suggested signs of cognitive decline.

“The main way to diagnose dementia is that we see a deterioration from someone’s own baseline in these four areas: language, memory, behavior, and psychomotor performance,” Gartner said.

“He’s deteriorated since his last administration noticeably but now we’re seeing deterioration almost week over week. The rate of decline is accelerating,” Gartner said.

Trump has made several statements, including his mix-up over Iceland and Greenland, among other comments that have led to further unease around his health.

“The high-pressure job can also accelerate cognitive dysfunction,” Gartner added.