Kelly Sadler, a special assistant in the White House communications office, is said to have referred to the senator's deteriorating health in response to his objections to Trump's new CIA nominee.
A White House official mocked Senator John McCain's brain cancer at an internal meeting on Thursday, saying his opposition to President Donald Trump's CIA nominee "doesn't matter, he's dying anyway," according to media reports.
Kelly Sadler, a special assistant in the White House communications office, made the comments at a closed-door meeting attended by about two dozen staffers, The Hill newspaper said. The Washington Post also reported Sadler's remarks.
McCain's wife, Cindy McCain, responded in a tweet. "May I remind you my husband has a family, 7 children and 5 grandchildren," she said.
John McCain, 81, has been a frequent critic of Trump. In a memoir due to be released later this month, McCain accuses fellow Republican Trump of failing to uphold American values.
McCain was diagnosed with an aggressive form of brain cancer last year. He has been receiving treatment in his home state of Arizona and has been absent from the Senate for months.
A White House spokesman did not dispute the report, the Washington Post said.
"We respect Senator McCain's service to our nation and he and his family are in our prayers during this difficult time," the White House said in a statement, according to the Post.
On Wednesday, McCain, who was a prisoner of war in Vietnam and was tortured by his captors, issued a statement urging his fellow senators to vote against Gina Haspel for CIA director.
He said she failed in a Senate Intelligence Committee hearing to address his concerns about the agency's post-9/11 harsh interrogation program for terrorism suspects.
South Carolina Republican Senator Lindsey Graham, a close friend of John McCain, told CNN of the White House aide's comment, "Ms. Sadler, may I remind you that John McCain has a lot of friends in the United States Senate on both sides of the aisle. Nobody is laughing in the Senate."