Sen. John McCain John Sidney McCainThe Memo: Trump's strengths complicate election picture Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' Cindy McCain: Trump allegedly calling war dead 'losers' was 'pretty much' last straw before Biden endorsement MORE (R-Ariz.) will return to Washington in January after undergoing physical therapy and rehabilitation in Arizona, his office announced late Sunday.

As a result, McCain will not be in Washington for the GOP tax bill vote, which is expected to take place early in the week.

“He is grateful for the excellent care he continues to receive, and appreciates the outpouring of support from people all over the country. He looks forward to returning to Washington in January," McCain's office said.

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Republicans have won over two key votes for the measure, meaning they should have the razor-thin majority needed to pass the bill, even without McCain.

President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE said Sunday he believes McCain would return to Washington if Republicans needed his vote.

McCain received treatment at Walter Reed Medical Center last week for a viral infection, Dr. Mark Gilbert said in a statement on Sunday, adding that McCain is “responding positively” to his cancer treatment.

He left for Arizona on Sunday.

McCain announced in July he had been diagnosed with glioblastoma, an aggressive form of brain cancer. He has been undergoing treatment since.