The NSW Waratahs have lost five-eighth Berrick Barnes for their crucial Super Rugby clash with the Sharks in Durban on Sunday morning (AEST).

Barnes was diagnosed with a footballer's migraine by one of Sydney's top neurologists after NSW's bonus-point win over the Lions at the SFS last weekend.

He trained well during the week in Durban, but management has decided to rest him as a precaution following two other bouts of concussion for the Wallabies star this season.

"Berrick's keen and he's certainly not in the position he was after the knocks he took in the Reds or Brumbies games; he's probably at about 90 per cent," said NSW coach Chris Hickey.

"But, given what he's been through this year, we want to make sure he's absolutely at 100 per cent before we reconsider putting him back on the paddock."

Daniel Halangahu will move into the No.10 jersey with Eastwood fullback Ben Batger named on the bench.

The Waratahs are focusing on overcoming a physical onslaught from the Sharks as they look to consolidate their top-six status.

The fifth-placed Waratahs (45 points) have the Highlanders, Sharks (both 43) and Bulls (40) all trying to chase them down with four rounds remaining.

The Sharks, who have struggled for consistency after starting the season with four straight wins, are expected to challenge the Waratahs with an abrasive style of play.

"What we're concentrating on is really the physical side of it," Waratahs lock and acting captain Dean Mumm told AAP.

"The Sharks are an extremely physical side, they've got some wonderful ball carriers in Bismarck du Plessis and a number of other top forwards.

"With South African sides, if you don't front up physically then you're gong to struggle."

The South African leg of their campaign looms as a season-defining one for the Waratahs, who play the Bulls in Pretoria next week.

"If we do the job this weekend and the Waratahs lose to the Bulls, that puts them out," Sharks' coach John Plumtree said on his team's website.

Plumtree, whose side plays its last three games away to domestic rivals, said the Sharks couldn't afford to drop another match.

He will be missing Jannie du Plessis, Ryan Kankowski, Odwa Ndungane and Adrian Jacobs, but has regained the services of veteran front rower John Smit and No.8 Keegan Daniel.

Following the firestorm of comment on the Waratahs' style of rugby and the feisty fans' forum last week, Mumm wasn't unhappy to be out of Sydney.

"It's nice to get away and have time and do what we want to do, without everything on the periphery," Mumm said.

Lock Sitaleki Timani returns to the run-on side for a NSW team striving to build on successive home wins over the Rebels, Force and Lions.

"I think we've got some momentum, we had to earn our wins," Mumm said.

He emphasised the Sharks were exceptional at scoring off turnovers.

Coach Chris Hickey also stressed the need for his competition-leading defence to minimise mistakes and retain discipline to starve promising five-eighth Patrick Lambie of goalkicking opportunities.

"Our defence is going to have to be very good because they are a strong attacking side, " Hickey said.

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