The renowned resilience of NSW Test hooker Tatafu Polota-Nau is being tested with the durable rake in doubt for the Waratahs' Super 14 season home debut against the Sharks on Saturday.

Polota-Nau, who missed only two Super games in his first four seasons, injured his hamstring early on in the loss to the Bulls in Pretoria last Saturday.

The 24-year-old frontrower was headed for a scan on the afflicted area straight after arriving back in Sydney on Monday afternoon.

He was hopeful of playing against the Sharks at the Sydney Football Stadium, but his coach Chris Hickey was waiting until the results of the scan were determined on Tuesday.

"It's a hamstring strain fairly high, we're just not too sure to what extent, there's some doubt there," Hickey said at Sydney Airport.

"It actually happened quite early in the first half and he found he couldn't really stretch out, so we made the decision at halftime to put Damien Fitzpatrick on and he did a good job for us in the second half."

If Polota-Nau is ruled out against the Sharks, former Australian under-20s and schoolboys captain Fitzpatrick will deputise, with former Force hooker Luke Holmes set to make his Waratahs debut off the bench.

Hickey said Wallabies hooker Adam Freier was still about four weeks away from playing following back surgery, though he had started running this week.

The Waratahs coach was more optimistic about the fitness prospects of Test prop Benn Robinson, who took another shoulder knock against the Bulls.

"We are reasonably confident that will settle down by Saturday," Hickey said of Robinson's injury.

Recently recruited lock Cam Jowitt, who missed the Waratahs' two games in South Africa after suffering an ankle injury in the opening round clash against Queensland, is still another week from returning.

The Waratahs' forward stocks will be boosted by the return from a two-match suspension of Wallabies lock and flanker Dean Mumm.

The versatile forward can play in either the second or back rows, but Hickey was keeping mum about which position the Test star would slot into on Saturday.

Mumm played at blindside flanker against Queensland, but could find himself back in the second row this weekend, with Ben Mowen re-establishing himself in the No. 6 jersey in South Africa.

Hickey said he was unlikely to make any changes outside of ones forced by injuries, as he wanted to develop combinations.

Exciting young centre Rob Horne, who made a cameo return off the bench against the Bulls, following a series of hamstring injuries isn't ready to start yet, according to Hickey.

The coach lavished praise on 20-year-old lock Kane Douglas, who made his first two Super starts after debuting off the bench against Queensland.

"He's a player that's improved over the last 12 months and every time he's been given an opportunity to play he's performed," Hickey said of Douglas.

"It was a big challenge for a 20-year-old matching up against (Bulls skipper and Springbok lock) Victor Matfield, I thought he did great credit to himself."

Hickey said he expected the winless Sharks to provide a big challenge to his side.

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