Melbourne - Star flank David Pocock makes his likely return for Australian conference leaders Brumbies against defending Super Rugby champions Waratahs while code-hopper Sonny Bill Williams could be missing for the Chiefs this weekend.
Pocock is set to be eased back into action off the bench after recovering from an ankle injury, delaying his anticipated match-up with incumbent Wallabies captain Michael Hooper in a duel of Australia's top openside flanks.
The Brumbies lead the overall standings after five games, while the Waratahs have had a difficult start to their title defence losing two of their four outings.
Pocock has played just six games since the start of 2013 after two knee reconstructions and then injuring his ankle in the first round of this season where he was man of the match.
In his absence over the last few seasons, Hooper has established himself as the Wallabies' first-choice number seven, but Pocock's return will spice up competition for openside flank.
The Waratahs' shaky defence faces another test at Sydney's Allianz Stadium on Sunday, with the Brumbies having scored a tournament-best 19 tries in their surge to the competition lead.
Coached by Waratahs' Michael Cheika's newly-appointed Wallabies assistant Stephen Larkham, the Brumbies have also conceded three tries in five games this campaign.
"The Brumbies are a very well drilled team," Waratahs hooker Tatafu Polota-Nau said.
"They do everything well and our focus on Sunday will be on playing consistently throughout the whole match and delivering a full 80-minute performance, which we haven't managed yet."
Williams has been struggling with concussion and is unlikely to play for the fourth-placed Chiefs against sixth-placed Coastal Sharks in Durban on Saturday.
Inside centre Williams, who returned to Super Rugby from Australia's National Rugby League this year, clashed heads in last week's match with the Western Stormers in Cape Town and has been subsequently struggling with symptoms.
"Sonny took a pretty severe head knock and hasn't been feeling so good for the last couple of days," Chiefs assistant coach Tom Coventry said.
"He hasn't recovered as quickly as we would have liked. He's had a few headaches. He's under a bit of a selection cloud this weekend."
The Chiefs fought back to end the Stormers' unbeaten start to the season with a 28-19 win last weekend and have won on four of their seven visits to Durban.
The Sharks have suffered a setback with Springbok lock Pieter-Steph du Toit ruled out for three months after knee surgery this week.
All Blacks lock Jeremy Thrush will make his first start of the season for the in-form Hurricanes against Highlanders in Dunedin on Friday.
Thrush, seeking a World Cup berth, missed the first three games of the season with a calf injury and another All Black returns in the Hurricanes backline, where Cory Jane takes Matt Proctor's spot on the right wing.
The Highlanders, trailing the Hurricanes by four points in the New Zealand conference, will be without their three most highly-rated props and their only two specialist openside flanks.
Ma'afu Fia is out for the season with ruptured knee ligaments, Kane Hames is serving a five-week suspension and Ross Geldenhuys broke a thumb during the win over the Waratahs last weekend.
Flanker Shane Christie remains sidelined after re-injuring his hamstring while John Hardie has a dislocated ankle.
"The Hurricanes are unbeaten, injury-free and at full-strength. They're now a very structured and organised team and Ma'a Nonu is playing his best Super Rugby for some seasons," Otago coach Jamie Joseph said.
"There are a lot of in-form All Blacks and they are a much-improved team."
In this weekend's other games, the Rebels host South Africa's Golden Lions in Melbourne, Crusaders face the Cheetahs in Christchurch and the Northern Bulls take on Australia's Western Force in Pretoria.
Blues, Reds and the Stormers have byes.
Brumbies: 15. Robbie Coleman, 14. Henry Speight, 13. Tevita
Kuridrani, 12. Christian Lealiifano, 11. Joseph Tomane, 10. Matt Toomua,
9. Nic White, 8. Ita Vaea, 7. Jarrad Butler, 6. Scott Fardy, 5. Sam
Carter, 4. Rory Arnold, 3. Ben Alexander, 2. Stephen Moore, 1. Scott
Substitutes: 16. Josh Mann-Rea, 17. Ruan Smith, 18. Jean-Pierre Smith,
19. David Pocock, 20. Jordan Smiler, 21. Michael Dowsett, 22. Lausii
Taliauli, 23. James Dargaville