NSW Waratahs No.8 Wycliff Palu could be sidelined for a couple of weeks, but centre Rob Horne is a confirmed starter for Friday night's Super Rugby opener against the fledgling Melbourne Rebels.

Palu has been ruled out of round one with a troublesome hamstring injury, which coach Chris Hickey confirmed may keep him out for a couple of weeks.

However, the Waratahs received a boost with Horne named in the run-on side and prop Benn Robinson included on the interchange bench.

Horne is back from an elbow problem and although he'll wear the No.13, Hickey indicated on Wednesday the 21-year-old will be eased back with limited game time.

Robinson didn't play in either of the Tahs' trial matches due to a calf problem and he'll gain match fitness coming on as a fresh reserve.

Hickey said uncertainty over the availability of his players hasn't been a distraction for the team as they prepare for the unknown of the Rebels.

"We couldn't be happier with Rob's progress. He's ticked all the boxes throughout the rehab and on Wednesday he showed us enough to prove he's not far off his best again.

"Benn's also done everything asked of him but given he hasn't had a hit-out yet and Sekope Kepu has performed really well in the trials, we think this is the best line-up to put out on Friday.

"We've had some trials and during those trials we've played players in different positions and everything else like that so I don't think it's a disruption.

"We're confident with the players we've got and the depth.

"Not knowing as much (about Melbourne) means you keep the focus on yourself and the reality is all we can control is how we play."

A bulked-up Ben Mowen will assume Palu's No.8 jersey and is confident his extra size can improve his effectiveness at the back of the scrum.

Mowen has increased from 102 to 114kg and is confident his defence and tackle-breaking ability has improved.

Palu missed most of last season with knee ligament damage and must now shake a hamstring injury on his opposite leg before he can return to action.

While it's a frustration for the giant 28-year-old, Hickey confirmed Palu won't be rushed back.

"It's hard to say with hamstrings, it'll probably be a couple of weeks I think," he said.

"With a long season ahead of us, he's an important player for us so we've got to make sure he's 100 per cent when he comes back and it doesn't become a chronic injury he's trying to deal with for the rest of the season."

Dave Dennis will start the match in Mowen's usual position on the side of the scrum.

Hickey is expecting the Rebels to utilise their size in the midfield and play a direct game and said he's wary of a few trick shots from their experienced coach Rod Macqueen.

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