A-League leaders Adelaide United might be forced into a late defensive reshuffle for Sunday's intriguing clash with defending champions Brisbane with an ill Cassio in doubt.The Reds have serious concerns about the Brazilian-born fullback after he was struck down by a stomach bug heading into the Suncorp Stadium encounter.Coach John Kosmina on Saturday admitted he was preparing to move Anthony Golec to left back if the in-form Cassio was ruled out and promote Nigel Boogaard.Adelaide's defence has been a bedrock of their success so far this season, conceding just three goals in their four matches.Cassio's scare comes as the Roar welcome back dangerous right back Ivan Franjic who has been a key to their past two titles with his speed and ability to overlap down the right side.While Franjic has been missed due to an abdominal problem, young defender Jack Hingert was among Brisbane's best in their shock 1-0 loss to Western Sydney.But coach Rado Vidosic had no doubts Franjic would provide a significant boost to a side who have only enjoyed one win this season - a 5-0 rout of Melbourne Victory."He knows our game inside out and (left back) Shane Stefannutto and Ivan have been very important to our attack, not just our defence," Vidosic said."Jack's done a good job and we're looking forward to re-signing him in years to come but, at the moment, we're looking for the experience that Ivan gives us."Brisbane have proven to be an A-League bogey side for Adelaide who haven't beaten the Roar since February 2010.But they did pull off a 1-1 draw in their last trip to Suncorp Stadium in January thanks to a brilliant Iain Ramsay goal and also enjoyed a 6-2 trial win in the pre-season.We're going into it quite confident," said Kosmina. "Provided we do the simple things and do them well, then I don't have a problem playing Brisbane."It's always good to test yourself against the best."However Kosmina felt the match would provide a better yardstick for the Roar and denied his side were under extra pressure as the competition pace-setters."If we're still top with four games to go then there may be a little bit more pressure but, at the moment, it's just about playing."