Sen. John McCain flew home to Arizona on Sunday and will miss a vote on the Republican tax bill that is expected early this week.

In a statement, the 81-year-old lawmaker said he would undergo rehabilitation and physical therapy there after being hospitalized at Walter Reed Medical Center, near Washington.

McCain — who was diagnosed with brain cancer earlier this year — said he would not return to Washington D.C. until January.

In a statement, Dr. Mark Gilbert, Chief of Neuro-Oncology at the National Institutes of Health, said that McCain responded well to treatment at Walter Reed for a viral infection.

"An evaluation of his underlying cancer shows he is responding positively to ongoing treatment," Gilbert said.

Earlier Sunday, after speaking with McCain's wife, Cindy, President Donald Trump told reporters that McCain was having a "very tough time." Trump added that the senator would return to Congress if he's needed for a vote on the tax bill.

"He'll come if we ever need him to vote," Trump said. "Hopefully we won't.

Republicans can only lose two votes on the $1.4 trillion bill. On Thursday, two holdouts — Sen. Marco Rubio, R-Fla., and Sen. Bob Corker, R-Tenn. — said they’d support the plan after initially opposing it.

Republicans are on a tight deadline. Democrats have criticized the plan as a giveaway to large corporations and the wealthy, and no member is expected to support it. The party’s latest addition to Congress, Sen. Doug Jones of Alabama, will leave the GOP with one fewer vote in the Senate after he takes office next month.