Fitness concerns surround Australia's Ryan Harris and Shane Watson Ryan Harris attempts to run out Kevin Pietersen off his own bowling. Darren Lehmann's commitment to shelving Cricket Australia's controversial rotation policy is set for the biggest test of his short reign heading into the Ashes finale in Sydney. As the fourth Test reaches a potentially thrilling climax on Sunday, Australian selectors are facing the balancing act of finishing a triumphant series on a high without compromising the team's hopes for the tour of South Africa. The biggest concerns surround Ryan Harris and Shane Watson, who both showed signs of weariness on the third day of the fourth Test at the MCG. Selectors will be wary of risking both players in the fifth Test in Sydney - a dead rubber - starting on Friday, for fear of them breaking down and missing the start of the series against South Africa in less than seven weeks. Take that: England's Stuart Broad is caught by Australian captain Michael Clarke as wicketkeeper Brad Haddin celebrates. They would not want a repeat of the fifth Test in England when Harris injured a hamstring and was sidelined for two months. Harris was not as potent in the second innings compared to previous Tests and, with 10 overs, was sparingly used by Michael Clarke. Mitchell Johnson and Peter Siddle bowled 39 and 38 overs respectively in Melbourne which is well below the zone where CA is concerned, though their fitness will also be closely monitored. Doug Bollinger and uncapped West Australian quick Nathan Coulter-Nile are likely to push for selection if Harris is ruled out, while James Faulkner, a squad member for all four Tests, will be in the frame, particularly with the worries over Watson. Watson, somewhat surprisingly, returned to the bowling crease on Saturday just two days after limping off the field with a groin strain, though he appeared far from comfortable. His first delivery was at a relatively pedestrian 120km/h and his speed for the rest of his four-over spell either side of lunch was only marginally higher. Managing Watson, who has had a history of injury, is considered one of the highest priorities for CA's medical staff. The all-rounder's dependable seamers have been considered an important, if underrated, component of Australia's rampant attack this series. "It's unfortunate he's had a career riddled with injury, he's probably our biggest challenge," CA team doctor Peter Brukner told the ABC. He's played every Test this year [apart from Mohali] and can usually get over his injuries a bit quicker now. Australia's injury worries have coincided with the most closely fought Test in a one-sided series. They also come less than a fortnight after a gruelling match in Perth's oppressive heat which pushed into the second session of the fifth day. The rotation policy, or informed player management, was widely criticised last summer but has not been used since Lehmann replaced the ousted Mickey Arthur in June. Lehmann has repeatedly stated his opposition to the idea, saying players will play if fit.