Updated

Republican Sen. John McCain, tweeting for the first time since returning to Arizona for treatment, said Monday he’s feeling better and plans to come back to work after the holidays.

The six-term U.S. senator is in Arizona after being hospitalized for a viral infection while battling brain cancer.

He tweeted, “Thanks to everyone for your support & words of encouragement! I’m feeling well & looking forward to returning to work after the holidays.”

McCain will miss the crucial Senate vote on the $1.5 trillion Republican tax package slated for later this week. The House is expected to vote Tuesday and the Senate on Wednesday, though the timing is fluid. If approved, it will be President Trump’s first major legislative win since taking office 11 months ago.

Trump said Sunday he had spoken to McCain’s wife, Cindy. He added that Sen. McCain will come back to Washington early if his vote is needed to pass the Republican tax overhaul.

“He's going through a very tough time, there's no question about it,” Trump told reporters. “But he will come back if we need his vote."

The 81-year-old senator will undergo physical therapy and rehabilitation at the Mayo Clinic in Arizona after spending several days at Walter Reed National Military Medical Center in Maryland.

Dr. Mark Gilbert, chief of neuro-oncology at the National Institutes of Health's National Cancer Institute, said in a statement that “McCain has responded well to treatment” and that “an evaluation of his underlying cancer shows he is responding positively to ongoing treatment.”

McCain underwent surgery in mid-July to remove a two-inch blood clot in his brain after being diagnosed with glioblastoma.