NSW flyhalf Lachlan MacKay has arrived back in Sydney hellbent on reclaiming the Waratahs No.10 jumper he has lost due to injury.

MacKay flew home from Durban after suffering rib cartilage damage in Saturday night's 36-13 Super 12 victory over the Sharks, and will visit a specialist in the coming days to determine the extent of the injury.

It's a tough break for the 22 year-old, who was injured in only his second game for the Waratahs.

"It's frustrating because I was really warming to the role," MacKay said.

"In the first game (against the Chiefs) I was just concentrating on getting through the match, but against the Sharks I really felt comfortable and was starting to inject myself more.

"So to hand over the opportunity now is especially hard."

MacKay was instrumental in getting the Waratahs off on the right foot early against the Sharks, making a 40-metre break to set up NSW's first try before leaving the field just before half time.

"I actually hurt it around 25 minutes in," he said.

"I tried to play on, but in the end I had to go off."

Inside centre Shaun Berne, who moved into flyhalf when MacKay went off against the Sharks, and replacement player Tim Donnelly will fight it out for the starting job against the Cats in Johannesburg this weekend.

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