Parton, in a letter Friday to Grand Ole Opry General Manager Pete Fisher, said she had visited Wagoner, The Nashville Tennessean reported. She described the 80-year-old Wagoner as "weak and not feeling great" but "in good spirits."
"He wanted to thank everybody for their thoughts and prayers," Parton said. "He’s looking forward to getting better and getting back to the Grand Ole Opry. I promised him I’d sing with him his first night back!"
Wagoner -- a member of the Opry for 50 years -- began his career with the Blue Ridge Boys singing on a Missouri radio station, and starred in "The Porter Wagoner Show" on TV from 1960 to 1979. Parton became an international star during her seven years on the show.
Wagoner suffered a near-fatal stomach aneurysm in 2006, CMT.com reported.
He released a new album this year, "Wagonmaster," to critical raves. He promoted the project by appearing with such contemporary acts Neko Case in Hollywood and the White Stripes at New York's Madison Square Garden.