"I visit him at least two or three times a week," Thomas said. "He's doing very, very well. He's doing a lot better than he was [when] he was in New York City."
Thomas, the Bills' running back from 1988-99, is returning to Buffalo early this week after spending the weekend at the Kentucky Derby and the Pro Football Hall of Fame FanFest in Cleveland.
Thomas, who still lives in the Buffalo area, has made it a routine to visit Kelly, who continues chemotherapy and radiation treatments after being diagnosed with a recurrence of oral cancer earlier this year.
After beginning his treatments in the New York City area, Kelly returned to Buffalo for Easter and hasn't left.
The Hall of Fame quarterback and his wife, Jill, posted a brief video on Facebook last week updating his condition.
"I'm just getting ready to go to my 19th treatment for radiation and I've already had two bouts of chemo," Kelly said in the video. "Keep those prayers coming. I sure need them. Without you, I wouldn't be able to get through this."
Marv Levy, who coached Kelly and the Bills to four consecutive Super Bowls in the early 1990s, said Kelly's condition has improved recently.
"Lately I've been in touch with family and they've kept my apprised," Levy said Saturday. "They said he has reacted better to some recent chemo treatments. He's back home. Feeling a little more upbeat."