Pictures from the historic first flight between Israel and the United Arab Emirates on August 31, 2020.
Asked about O'Brien, Trump told reporters he had not seen the adviser lately and did not know when he had tested positive.
After Trump over the weekend said he was not briefed on the matter, the White House said Trump was not "personally" briefed but did not address whether he had received a written report.
"I have worked long & hard with Robert. He will do a great job!" Trump wrote on Twitter.