CNN’s Dr. Sanjay Gupta, a brain surgeon, said President Biden’s debate performance was “concerning” from a medical standpoint and called on the president to undergo cognitive and neurological testing in an op-ed published Friday.

Gupta said he was not alone in his concern over the president’s mental state, reporting that he received “more than a dozen calls, texts, and emails from medical colleagues” following the debate.

“From a neurological standpoint, we were concerned with his confused rambling; sudden loss of concentration in the middle of a sentence; halting speech and absence of facial animation, resulting at times in a flat, open-mouthed expression,” he wrote.

Shortly after the debate, campaign aides said the president was suffering from a cold on the day of the debate. White House press secretary Karine Jean-Pierre added Wednesday, nearly a week after the debate, that Biden had jet lag following his overseas trips earlier in the month.

Gupta did not challenge the White House’s explanations, but he questioned Jean-Pierre’s statement that cognitive tests were deemed “not necessary” by the president’s medical team.

“There are definitely aspects of cognition that decline as we age — especially fluid abilities like processing speed, attention span and memory. This is normal and expected and doesn’t necessarily stand in the way of someone’s ability to do their job,” he wrote.

“But for a minority of us, that decline is steeper and can lead to dementia,” he continued. 

Gupta noted parts of both former President Trump's and Biden’s medical history indicated risk factors for cognitive decline, including Biden’s experience with brain aneurysms and that Trump’s father passed from Alzheimer’s disease when he was 93.

He also acknowledged that Trump, at times, displays the “same signs as Biden, including nonsensical rants as well as confusing names and current events.” Gupta noted that Trump has taken cognitive tests, but he critiqued the rigor of his tests and stated that the memos about his health “used hyperbolic language, unusual for medical documentation.”

Gupta noted the Biden administration has rejected requests from the press to release the president’s medical records. 

“We often hear that observing a candidate on the campaign trail is the best assessment of the individual’s physical and cognitive health,” Gupta wrote. “The country is watching now, and that assessment gives cause for concern — and a need for transparent testing."

The Biden campaign did not immediately reply to request for comment.

Dr. Anthony Fauci, the former medical adviser to both Trump and Biden, last week warned against diagnosing Biden based on the debate alone. But he said he had "no doubt" that Biden is capable of continuing as president.

“Did he have a bad cold, you know? Did he take an antihistamine to make him, you know, groggy, or what have you? We don’t know what went on,” Fauci said of the debate. “And I think it would be unfair and inappropriate to try and diagnose something from just a 90-minute clip.”