The broadcaster said the superstar golfer's half-brother Kevin Woods, 54, of San Jose, Calif., is in the advanced stages of the disease. He is reportedly wheelchair-bound, has failing vision and can barely move his left arm.
His brother, Earl Woods Jr., said Tiger Woods -- who shares a father with Kevin, Earl Jr. and Royce Woods -- hasn't responded to requests to help Kevin obtain a caregiver.
"I leave messages," Earl Jr. told ESPN. "I leave updates on Kevin, but for whatever reason I don't get a response. … Kevin loves Tiger. A call from Tiger would really pump Kevin up. When he doesn't call, it just makes him feel worse."
The broadcaster said Woods, who is preparing to play in The Masters this week, wouldn't comment on the situation.
The three siblings are much older than Tiger Woods and are the offspring of Earl Woods Sr. and his first wife, Barbara Gary of Kansas.
The golfer's mother is Woods' second wife, Kultida Punsawad.
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