The 26-year-old has won 50 caps for the Wallabies playing at flyhalf, centre and fullback and the loss of the goalkicker, who was a mainstay of the side last year, would be a blow to Australia coach Robbie Deans.
The report said that Barnes would not be allowed to leave for Japan before his contract expires at the end of the year, with Warathas coach Michael Cheika remaining hopeful he can hang on to the key figure.
"No one says sayonara until they've left," the coach said in Sydney on Thursday ahead of the start of the 2013 Super Rugby season next month.
Australia host the British and Irish Lions in a three-test series in June and July before taking part in the Rugby Championship against New Zealand, South Africa and Argentina in August after the conclusion of the Super Rugby campaign.
The Wild Knights are quickly building a reputation for securing the leading names in world rugby after paying a reported $1 million to All Black poster boy Sonny Bill Williams to play 12 matches last year.