Bishop Nonyane of the South African township of Tembisa diagnosed the cause of Kewell's groin problems, achilles injuries, blood infection and gout as evil spirits, the Australian Daily Telegraph reports.
Nonyane said: "No-one has bewitched him. But it is because of malicious spirits, and the main intention of those malicious spirits is to hurt him.
"Because we can't perceive these malicious spirits, our naked eye says it's bad luck. But his injuries are because of the malicious spirits, and they in turn are hurting him.
"His bloodline has been tormented by these spirits and, nowadays, these spirits are attracted to him. It happened centuries ago."
He added: "You must pray, and believe in prayer. A get well message from the prime minister will do. From the prime minister's mouth.
"Let the guy know that the whole Australian community rallies behind him to get well, and that they do believe in him, to get well."
According to AFP, Rudd later appeared on Channel Seven's Sunrise to back Kewell, who is the husband of Hollyoaks actress Sheree Murphy.
"I think Harry's fantastic, and I wish him the absolute best - and I'll be out there watching on Monday for the first game," he said.