John McCain set for Senate return on Tuesday following cancer diagnosis It was announced last week McCain has been diagnosed with brain cancer.

 -- Following the announcement last week that he has brain cancer, Senator John McCain, R-Arizona, is set to return to the U.S. Senate on Tuesday, according to a statement from his office.

“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,” reads the statement released Monday night.

The Arizona senator's office and the Mayo Clinic Hospital in Phoenix announced Wednesday night that McCain had surgery on July 14 to remove a blood clot above his left eye.

"Subsequent tissue pathology revealed that a primary brain tumor known as a glioblastoma was associated with the blood clot," the hospital said in a statement. According to the hospital, McCain and his family are reviewing further treatment options, which may include a combination of chemotherapy and radiation.

McCain’s return will come as a vote is expected to start debate on the Senate’s beleaguered health care bill. With multiple Republicans seemingly undecided on how to proceed, the odds of Tuesday’s procedural vote passing are thin. Now, years of promises to repeal and replace the Affordable Care Act, also known as Obamacare, could come down to 80-year-old McCain.

McCain has indicated he would vote yes on a motion to proceed vote with the assurance that he can add amendments to the bill once it's on the floor. However, he has also expressed serious concerns about the legislation and isn't a guaranteed yes on a final version of the bill.

"Senator McConnell has been talking to [McCain]. I have not personally,” Senator John Cornyn told ABC News on Monday, prior to McCain’s announcement. “I know he’s chomping at the bit to come back. It’s just a matter of getting doctors’ approval,"

"It would help if he's here," Cornyn told us. "Ultimately, we want him back as soon as he can for obvious reasons."

ABC News' Dean Schabner contributed to this report.