Rebels utility Kurtley Beale could be in doubt for the first match of the Rugby Championship on August 18, the gifted back sustaining a fractured rib against Queensland in their last Super Rugby clash.

Melbourne's medical staff on Tuesday initially said Beale wouldn't be joining his teammates in South Africa for games against the Lions and Stormers after previously saying he was suffering "soreness" following the 32-17 loss to the Reds.

But later on Tuesday that was upgraded to a stint out of up to six weeks.

"Kurtley sustained a chest injury in the Wallabies Test against Wales in Sydney which appeared to settle quickly. However, on Friday night it was exacerbated in our match against the Reds. Further investigations revealed a rib fracture, which will take 4-6 weeks to heal and rule him out for the remainder of the Super Rugby season," Rebels coach Damien Hill said.

The Wallabies' first match of the four-nation series is against New Zealand at ANZ Stadium, in six weeks' time', leaving him touch and go to make the squad.

The Wallabies fullback went into the clash against the defending Super Rugby champions with bruised ribs suffered during the third Test against Wales in Sydney in his first match back from shoulder surgery.

Beale's operation at the start of June forced the 23-year-old to miss one Super Rugby game, the one-off Test against Scotland and the first two clashes with Wales.

Fellow Wallaby James O'Connor was also missing from the the 25-player Rebels squad which flew to South Africa on Sunday after straining his hamstring.