Australian backstroke champion Isaac Cooper has been banished from the looming Commonwealth Games for misusing medication.
Cooper has been sent home from the Australian swim team's pre-Games camp in Chartres, France.
"Cooper has been sent home from the Dolphins training camp following some wellbeing challenges, including the use of medication," Swimming Australia (SA) said in a statement on Wednesday.
"He has acknowledged his mistakes and accepted the consequences and Swimming Australia will continue to support him as he addresses these challenges."
Cooper has departed Chartres, where he had been for the past week with the rest of the swim team ahead of arriving in Birmingham next week.
A SA spokesman told AAP the sedative Stilnox was "categorically" not the misused substance.
Before the 2012 London Olympics, six Australian swimmers - Eamon Sullivan, Matt Targett, James Magnussen, James Roberts, Tommaso D'Orsogna and Cameron McEvoy - were sanctioned over the use of Stilnox at a bonding session.
All but Roberts admitted abusing Stilnox, a sleeping medication which had been banned by the Australian Olympic Committee.
The six swimmers were fined and given deferred suspensions by SA.
Cooper had been favoured to win gold medals in the 50m and 100m backstroke events at the Commonwealth Games in Birmingham starting on July 28.
The 18-year-old is the Commonwealth's top-ranked swimmer in both backstroke events and was also entered in the 50m butterfly and 50m freestyle.
"The welfare of our athletes remains our absolute priority," SA's statement said.
"Swimming Australia is vigilant in educating athletes of their obligations under the National Integrity Framework and will continue to provide all necessary support to ensure they uphold the highest standards and behaviours when representing Australia."
Commonwealth Games Australia chief executive Craig Phillips was informed of the decision to send Cooper home but awaiting more information from SA.
"Obviously a difficult decision to take and I know they (SA) certainly have some concerns for Isaac's wellbeing as well," Phillips said.
"Really, at this point we don't have any more details.'
Australian team chef de mission Petria Thomas said: "We have received some advice from Swimming Australia but just looking to clarify that before moving forward.
"It's obviously a challenging time for young Isaac ... it becomes really a wellbeing matter," she said.
"And we wish Isaac all the best while he takes the time to work on his wellbeing."
At Australia's selection trials in May, the Bundaberg-born swimmer set a national record in the 50m backstroke.
Last month, Cooper made the 50m backstroke final at the world championships in Budapest, finishing eighth.
He placed 12th in the 100m backstroke at the worlds and won a silver medal as a heat swimmer in Australia's 4x100 mixed relay team.
