A specialist has confirmed the worst for Wallaby flanker Phil Waugh, who will undergo surgery on Thursday and be out of rugby for at least three months.

Waugh injured his left ankle in the early stages of the Waratahs Super 14 match against the Cheetahs on the weekend with MRI results confirming medial ligament damage.

The 27-year-old, who returned to Sydney on Tuesday with the Waratahs following their three-match campaign in South Africa, will have the results assessed again by a radiologist but surgery is almost certain to go ahead.

He described his injury as a "a bit of a freaky thing and very disappointing."

"It was in the 37th second, someone (Cheetahs forward Juan Smith) just stood on my foot as I was putting all my weight on that leg and it just went underneath me."

Waugh has missed just five out of the Waratahs' 86 Super 14 matches.

"Frustrating but that's rugby, isn't it? I've had a pretty good run over the last four years, I've just got to make sure I come back in good shape.

Both Waugh and NSW coach Ewen McKenzie suggested youngster Beau Robinson had the inside running to take his starting spot in the Waratahs next game against the Force in a fortnight.

While McKenzie was disappointed at loosing Waugh, he said another Wallaby back rower, David Lyons, was set to return from injury for the Force fixture.

Lyons, who missed the Waratahs' first three Super 14 matches following a knee arthroscopy, is set to make his return for the NSW Academy side against Victoria in Melbourne this weekend.

McKenzie said the long standing Wallaby and Waratahs No.8 would probably play just 20-30 minutes this weekend.

"He's such an enthusiastic guy, we don't want him to over do it," McKenzie said.

McKenzie remained tight lipped about who would replace Waugh as captain, though he hinted he'd already made up his mind.

"I've got some pretty strong thoughts there, we will sort that out by Friday," McKenzie said.

The new skipper could come from one of the other three players in the NSW leadership group, hooker Adam Freier, centre Morgan Turinui and fullback Sam Norton-Knight, while Wallaby flanker Rocky Elsom could be another contender.

McKenzie wasn't too perturbed that the Waratahs could fall further behind the leading pack this weekend when they have the bye.

"It's a tight competition and it's going to go right down to the wire and every week there's going to be some changes," McKenzie said.

"That's why I don't feel stressed at the moment. We've got 10 games left and seven of them at home and we are the only team in the competition that hasn't played a home game yet."

McKenzie said while NSW was currently missing over 300 caps worth of experience through injury he liked bringing younger players into the team and Super rookies Robinson and five-eighth Kurtley Beale had brought enthusiasm to the side and had earned the respect of their more senior teammates.

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