President Trump, who's pressuring senators to pass some kind of bill, should send Air Force One to fetch McCain.
McCain's absence put the future of the GOP effort to pass a new health care bill in jeopardy because the party can not afford to lose votes.
In a message on social media on Wednesday, McCain said: "I greatly appreciate the outpouring of support-unfortunately for my sparring partners in Congress, I'll be back soon, so stand-by!" "Thank you all for your best wishes".
Yet fellow Republicans took McCain's return as a positive sign for Tuesday's vote.
McCain also said he would not vote for the current GOP version of the repeal-and-replace bill.
McCain, who was treated by doctors at the Mayo Clinic in Phoenix, had a malignant tumor associated with a blood clot removed from behind his left eye. During his 2008 presidential campaign, McCain corrected a woman at a New Hampshire town hall meeting who claimed Barack Obama was an Arab.
McConnell promised to bring a full repeal bill with a two-year delay to the floor, which President Trump seemed to be on board with. They've been unable to find a replacement plan that can attract at least 50 votes in the Senate, where the party has a 52-48 majority.
Senator Joe Manchin, a Democrat from West Virginia, took to Twitter and criticized Kelli Ward, who plans on challenging McCain's colleague, Jeff Flake, for his Senate seat next year.
"It is just extraordinary how upbeat he is and how accepting of his diagnosis - it was truly inspirational to talk with him", she said.
"I'm optimistic right now, based on the atmosphere, the sense that I have from members", said Sen.
McConnell encouraged senators to vote Tuesday to open what he said would be a period of "robust debate" on health care.
However, McCain has made no suggestion that he will be stepping down because of his health, and is not due to run for re-election until 2022. [People] like her aren't welcome in the US Sen, ' Manchin said.
"It's awfully hard when people climb the tree and get out on a limb and say, 'I'm going to vote no,"' the Kansas senator said.
Efforts to resurrect McConnell's Obamacare replacement suffered a further blow on Friday when the Senate parliamentarian issued a preliminary finding that key parts of the proposal don't qualify for a fast-track procedure being used by the GOP.
"I haven't received word from any of the feminists out there saying, 'Hey, what are you doing attacking a strong Republican woman?' I haven't received anything from any well-known Republican women either, which is kind of disappointing", she said.