(CNN) On a day that saw Donald Trump make headlines with his appearance on "The Dr. Oz Show," another doctor also offered a diagnosis.

"I think both (presidential) candidates should have what we call neuropsychologic testing," Dr. David Scheiner told CNN's Erin Burnett on "OutFront" Wednesday evening.

Best known for once being Barack Obama's doctor, Scheiner is supporting Hillary Clinton. He said he's concerned by her opponent's "erratic behavior."

"We know he's got a narcissistic personality disorder at the very least," said Scheiner. "But I sometimes wonder if he might even be hypomanic. But I think psychologic testing would be important for him."

Scheiner is a physician, not a psychiatrist. But clinicians are warned by the American Psychiatric Association against diagnosing public figures they haven't examined.