Charlie Austin launched an astonishing rant at boss Ralph Hasenhuttl after being frozen out, according to The Sun
His team-mates were stunned as the outcast striker accused the Saints manager of being 'disrespectful'.
The 30-year-old striker launched his tirade after being told he would not travel with the first team during pre-season.
Austin has been told to train with the Under-23s as the club try to offload him during the summer transfer window.
The striker, who has one year left on his current contract, has reportedly snubbed a move to West Brom.
Premier League new-boys Aston Villa are also interested in signing him.
Austin, who joined from Queens Park Rangers for £4million in 2016, deactivated his Twitter account on Tuesday amid doubts over his future.
Austin was left out of the pre-season training camp in Austria, along with wantaway midfielder Mario Lemina. Southampton drew 1-1 against SCR Altach in Austria on Sunday, with new signing Che Adams scoring.
Saints face Preston on Saturday before pre-season trips to Macau and Dublin.