Arizona Cardinals' Fitzgerald visits Sen. McCain at his Arizona cabin

— -- Arizona Cardinals wide receiver Larry Fitzgerald paid a visit Saturday to one of his team's biggest cheerleaders: Sen. John McCain.

"Look who came for a visit today. @larryfitzgerald," McCain's wife Cindy wrote on Instagram, along with a photo of the trio at the McCains' Arizona cabin. "Our favorite @azcardinals and a wonderful human being!"

Fitzgerald and the 81-year-old Arizona Republican lawmaker -- who has been battling an aggressive form of brain cancer for months -- have been friendly for years.

In December, the football player penned a touching tribute to McCain for Sports Illustrated.

"When I think about Christmas, and I think about Senator McCain, I think of giving," Fitzgerald wrote.

In a nod to McCain's military service, Fitzgerald continued, "The sacrifices John McCain has made for our country, and especially the men and women he served with in the military, are incredible. I saw the very jail cell where he was held as a POW and I tried to imagine what it must have been like to be him. I took a photo of myself next to his flight suit, the suit he was wearing when he got shot down. So powerful. So meaningful. Those images will never leave my mind."

And of McCain's health, Fitzgerald wrote, "Senator John McCain again finds himself in a battle. This time it’s with cancer, and the treatment he’s undergoing is exhausting. I'll wish him a Merry Christmas today, and I pray he lives another 20 years."

McCain was diagnosed with glioblastoma over the summer, and in July, he began chemotherapy and radiation treatment at the Mayo Clinic in Phoenix.

In December, McCain spent time in a hospital. "He’s receiving treatment for the side effects of the therapy, his longtime friend, Sen. Lindsey Graham, R-S.C., told ABC News at the time. "I feel pretty good about the way the treatment is affecting his underlying cancer. But the treatment has a downside. So he’s tryin’ to get rested up ... I’m very confident he’ll come back and continue to participate for a long time to come."

In an interview with the Arizona Republic last month, McCain's son Jack said of his dad, "He is a tough old person. I usually use the term 'bastard.' He's a tough old bastard. And he has an indomitable spirit. It is impossible to keep the man down."