Ryan O’Neal Cancer Fears — Shocking Photos

Ryan O’Neal — shrunken to an alarming 135 pounds in stark contrast to his beefy 2009 beach-going self — claims he needs emergency surgery for a bad back, but pals and medical experts fear that his cancer has returned in a savage fury and the "Love Story" hunk is facing the end!

The star — shown here dog-walking with his son Redmond — looked shockingly frail and wasted just after announcing he was canceling his appearance in a touring play in the England this fall because of the emergency operation. The National ENQUIRER has learned from an alarmed pal that Ryan has shriveled down to 135 pounds — dangerously low for the once-strapping stud.

“He looks terrible,” the pal says of Ryan, who lost his longtime love Farrah Fawcett to anal cancer in 2009. “This surgery has everyone close to Ryan fearing that — combined with cancer — it might write his death sentence!”

The 76-year-old skirt-chaser recently revealed he’s battled three different forms of the disease — skin tumors, Stage 2 prostate cancer, and chronic myelogenous leukemia. Two medical professionals believe he may be in grave danger – especially from a return of the leukemia, where the body produces white blood cells instead of red, gutting the immune system.

Dr. Gabe Mirkin, who hasn’t treated the "Barry Lyndon" star, says “if the white blood cells take over and knock off his red blood cells, then you get into dire trouble.”

Radiation oncologist Dr. Jerome Spunberg, who also hasn’t treated the actor, says Ryan — shown in his recurring role as Max Keenan on "Bones" — “might live for years with his leukemia, but it could require aggressive treatment.”

Meanwhile, his frail state and the sudden news of his “back surgery” terrifies the friends who've stuck with him through troubles with his kids, sordid accusations, and legal battles. “We’re just concerned whether he’s strong enough to pull through,” says a pal. “He’s not a young man. He’s already hobbled and using a cane.”