Sen. John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE (R-Ariz.) will miss this week's votes in the Senate after undergoing surgery on Friday, depriving Republicans of a key vote on healthcare.

McCain's absence means Senate Republicans almost certainly will not have the 50 votes they'd need to win a procedural vote.

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Sens. Rand Paul Randal (Rand) Howard PaulSecond GOP senator to quarantine after exposure to coronavirus GOP senator to quarantine after coronavirus exposure The Hill's Morning Report - Sponsored by National Industries for the Blind - Trump seeks to flip 'Rage' narrative; Dems block COVID-19 bill MORE (R-Ky.) and Susan Collins Susan Margaret CollinsJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally Momentum growing among Republicans for Supreme Court vote before Election Day MORE (R-Maine) have already said they would oppose the procedural vote. With all Democrats voting no, that would leave Republicans with just 49 votes, given McCain's absence.

A further delay in the schedule is bad news for Senate Republicans, as it will allow opponents of the legislation more time to pressure wavering GOP centrists to vote against it.

Even with McCain, it is uncertain whether Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellMomentum growing among Republicans for Supreme Court vote before Election Day Trump expects to nominate woman to replace Ginsburg next week Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral MORE (R-Ky.) could put the 50 votes together for the bill.

An analysis and score of the Senate GOP's new healthcare bill from the Congressional Budget Office is expected on Monday.

Centrist GOP Sens. Rob Portman Robert (Rob) Jones PortmanRomney undecided on authorizing subpoenas for GOP Obama-era probes Congress needs to prioritize government digital service delivery House passes B bill to boost Postal Service MORE (Ohio), Shelly Moore Capito (W.Va.), Lisa Murkowski Lisa Ann MurkowskiMomentum growing among Republicans for Supreme Court vote before Election Day Collins: President elected Nov. 3 should fill Supreme Court vacancy Barrett seen as a front-runner for Trump Supreme Court pick MORE (Alaska) and Dean Heller Dean Arthur HellerOn The Trail: Democrats plan to hammer Trump on Social Security, Medicare Lobbying World Democrats spend big to put Senate in play MORE (Nev.) are among the swing votes.

Portman and Heller also face pressure from Republican governors in their states who are worried the Senate bill's curtailing of federal support for ObamaCare's Medicaid expansion could hurt their constituents.

McCain's office in a statement said he is doing well after undergoing surgery to remove a blood clot from his eye on Friday.

“Senator McCain received excellent treatment at Mayo Clinic Hospital in Phoenix, and appreciates the tremendous professionalism and care by its doctors and staff. He is in good spirits and recovering comfortably at home with his family. On the advice of his doctors, Senator McCain will be recovering in Arizona next week," the statement said.

Senate Majority Leader Mitch McConnell (R-Ky.) announced this week he was extending the Senate's sessions for two weeks, cutting the August recess short. That could give his conference more time to get healthcare done.

McCain, 80, had the procedure done at the Mayo Clinic Hospital in Phoenix following an annual physical.

"Surgeons successfully removed the 5-cm blood clot during a minimally invasive craniotomy with an eyebrow incision. Tissue pathology reports are pending within the next several days," the statement from the Mayo Clinic read.

“The Senator is resting comfortably at home and is in good condition. His Mayo Clinic doctors report that the surgery went ‘very well’ and he is in good spirits. Once the pathology information is available, further care will be discussed between doctors and the family," the statement said.