Senator John McCain, R-Ariz., will return to the Senate on Tuesday -- the day of a crucial vote to open debate on legislation to repeal and replace ObamaCare, his office announced on Monday night.

McCain, 80, has been recovering at home in Arizona following a brain tumor diagnosis.

“Senator McCain looks forward to returning to the United States Senate tomorrow to continue working on important legislation, including health care reform, the National Defense Authorization Act, and new sanctions on Russia, Iran and North Korea," his office said in a statement.

With McCain's return - and barring any other absences - there will now be a full complement of senators on hand for the health care test vote.

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That includes 52 Republicans and 48 senators who caucus with the Democrats. Republicans can lose only two votes and have Vice President Pence vote to break the tie and start debate.

A tweet from McCain's account Monday night read: "Look forward to returning to Senate tomorrow to continue work on health care reform, defense bill & #RussiaSanctions."

McCain was diagnosed with a brain tumor following a July 14 craniotomy to remove a blood clot from above his left eye, the Mayo Clinic Hospital in Phoenix said last week.

The hospital's examination of the tissue revealed that a primary brain tumor, know as a glioblastoma, was associated with the blood clot.

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Earlier Monday, Senate Majority Whip John Cornyn, R-Texas, discussed plans to get McCain back to the Senate.

"They were trying to get approval [from his doctors] for his travel arrangements. I've personally volunteered to rent an RV," Cornyn said, according to Politico.

Fox News' Chad Pergram and The Associated Press contributed to this report.