Rubio made the comment while talking to reporters at the Republican National Convention in Milwaukee following the news that Biden had been diagnosed with COVID-19, the report said.
"The question is, if he's not going to be their nominee because he's not up to it, how can he be our president for the next six months?" the report quoted Rubio as saying. "If there's something wrong with you that doesn't allow you to run for president, how can you still be there as president? If they're going to remove him as a nominee, they’ve got to remove him as president, and that's really bad for our country."
Rubio also noted that he is worried about who is actually running the United States if the Democrats knew about Biden's cognitive decline and deliberately hid this fact from the public.
"They knew Joe Biden — I don’t mean this to be cruel, but they knew the condition that he was in, and they deliberately hid it from the world. And it makes you wonder who's running our country. That's what I worry about," the senator said.
At the same time, Rubio said he does not see how the Democratic Party could bypass Vice President Kamala Harris if Biden withdraws from the race.
Numerous Democrats have called on Biden to end his campaign and step aside for an alternative nominee, following a dismal debate performance against Republican nominee Donald Trump last month.
The Biden campaign has said that they are not planning for a scenario in which Biden is not the Democratic presidential candidate.