Australian swimmer and Commonwealth Games gold medal favorite Isaac Cooper has been ruled out of the competition for disciplinary reasons. The 18-year-old will not compete "following some wellbeing challenges, including the use of medication", Swimming Australia (SA) announced. He will also be sent home from a training camp in France. Cooper was the top ranked backstroker due to compete at the Games in Birmingham, which start on 28 July. Along with the 50m and 100m backstroke events, he was set to line up for the 50m butterfly and 50m freestyle races. In a statement, SA said it is "vigilant" in making sure athletes uphold the highest standards and behaviours when representing Australia. "He has acknowledged his mistakes and accepted the consequences, and Swimming Australia will continue to support him," it said. "The welfare of our athletes remains our absolute priority." SA says the medication involved is not Stilnox, The Sydney Morning Herald reports. Six swimmers were famously fined by SA after using the drug in a "bonding session" before the 2012 Olympic Games. Cooper made his Olympic debut in Tokyo last year, finishing 12th in the 100m backstroke and winning a bronze medal as part of the mixed 4x100m medley relay team. At the Fina World Championships in Budapest last month, he finished eighth in the 50m backstroke and 12th in the 100m - behind swimmers from countries outside the Commonwealth. He also won a silver medal as part of the Australian mixed medley relay team. Tim Disken - a reigning Commonwealth Games champion in the 100m freestyle S9 and 100m Breaststroke SB8 - has also been ruled out, due a setback in his recovery from a recent surgery. — BBC