Toby Keith's Health Struggle: The Country Singer's Desperate Fight For His Life After Stomach Cancer Diagnosis

But a burning desire to play for fans at least once more led the patriotic performer to do an hour-long impromptu set at Jeff Rudy's Steakhouse in Lexington, Ky., on November 4.

"Toby was in Kentucky for his beloved Breeders' Cup horse races and decided he needed to get back in the saddle himself and pull off a show," a friend revealed. "He wanted to prove to himself that he could still do it."

But Toby's skeletal frame, sunken eyes, and slouching posture sent alarming signals. "He's more than four months removed from his treatments, but you can tell his body isn't recovering," confided the pal. "You really fear the worst for him."

Florida-based oncologist Dr. Jerome Spunberg, who has not treated the Courtesy of the Red, White and Blue singer, said Toby is facing a desperate fight for life.

"He looks like he has lost well over 50 pounds," noted Spunberg. "He likely had a partial or full gastrectomy to treat his stomach cancer, and that really mitigates your capacity to eat enough to put on weight. It's not a good sign. He should be putting on weight by now."

Although Spunberg said Toby's ability to perform "shows he has energy," his long-term prognosis is bleak. "Stomach cancer is generally fatal," he explained. "The survival rate is very low. Many patients die within two years of being diagnosed."

Still, the brave balladeer is telling friends not to write him off.

"Toby has dealt with a lot of adversity in his life to get where he is today, so he isn't giving up now," said the friend. "He sees his Kentucky show as the beginning of a comeback, not the end of the road."