Rob HouwingCape Town – Experienced fetcher George Smith leads the Brumbies into battle against the high-riding Sharks in the Super 14 match at Absa Stadium on Saturday – their third captain in as many weeks.The Australian newspaper reported on Thursday that physical centre and acting leader Stirling Motlock remains no more than a 50-50 chance to play, after suffering a knee injury in the 25-17 defeat against the Lions in Johannesburg.A week earlier, regular captain Stephen Hoiles was also injured in the bruising derby against the Waratahs.Although Smith has already been named as skipper, the paper said coach Andy Friend would give Mortlock, pencilled into the XV, until match day to prove his fitness: “Given he’s such a quality footballer we’ll give him up until the last hour,” Friend was quoted as saying.Mortlock himself added: “It needs to improve in the next day and a half or I’m at long odds, I would say.”The Brumbies are rather falling off the pace in ninth position and need to register the upset win to revitalise their challenge.But recent history is in their favour, with a tidy treble of victories against these opponents: they beat the Sharks 27-21 in Canberra last year and even prevailed in Durban in 2007 (21-10) when the Sharks topped the table but lost in the final to the Bulls.The 2006 meeting in Australia also went the way of the Brumbies (35-30) and you have to go back to 2005 for the last Sharks win (36-24 at home).Brumbies:15. Mark Gerrard, 14. Adam Ashley-Cooper, 13. Stirling Mortlock, 12. Tyrone Smith, 11. Clyde Rathbone, 10. Christian Lealiifano, 9. Joshua Holmes, 8. Julian Salvi, 7. George Smith (captain), 6. Mitchell Chapman, 5. Mark Chisholm, 4. Ben Hand, 3. Guy Shepherdson, 2. Stephen Moore, 1. Ben Alexander.Replacements - from: Huia Edmonds, Salesi Ma'afu, Shawn Mackay, Peter Kimlin, Patrick Phibbs, Gene Fairbanks, Alfi Mafi, Matt ToomuaMeanwhile, the Perth-based Western Force are chasing the signature of burly Waratahs prop Matt Dunning.Dunning was forced to sit out the current Super 14 with a snapped Achilles tendon, and it appears he has fallen down the front-row pecking order in Sydney anyway.