Da Costa (26) failed to show up for Southern's game against the Wellington Phoenix development team in Wellington last weekend, after he was told he would not be starting last Friday, coach Mike Fridge said.
''He wasn't happy about that and he just didn't turn up,'' Fridge said yesterday.
''The last time I spoke to him was when I told him he was on the bench. Initially, he accepted the decision, then a few hours later the text messages started flying back and forwards that he didn't accept it and that he felt he should be back in the team.
''I said, 'Well, no, nobody is bigger than the club. If players come in and they do well they deserve to keep their place in the team.
''He didn't accept that because he felt he was the best player in the team and when he is available he just walks straight back into the side.''
Trouble started brewing when the French midfielder ''faked'' an injury against Auckland City a fortnight ago.
''He has admitted that he wasn't injured against Auckland City,'' Fridge said.
''He faked the injury for whatever reason.''
After da Costa's no-show left Southern United a man short last weekend, Fridge went to the United board and said he did not want the midfielder in his team.
''As far as I'm concerned, he let the club down, he let the players down and he let the coaches down.
''I'm not having anybody thinking they are bigger and better than everybody on the team.''
Da Costa is understood to have flown back to Paris yesterday morning and was not available for comment.
His profile on the team's official website has been removed, and striker Tom Jackson has been named captain.
Southern United chairman Aaron Joy declined to go into specific details, but said the team had ''no choice but to move on'' from da Costa.
Jackson, the new captain, was aware of da Costa's departure but was not ''personally aware'' of any issues between Fridge and the Frenchman.
The stand-out striker has nabbed six goals this season and just wants to concentrate on finishing the season strongly.
''There's a few games left, so hopefully we can get some points, encourage the guys, get some momentum and improve morale, I suppose,'' Jackson said.
After starting the season with two wins in the first three rounds, Southern has lost eight of its last nine matches and has just seven competition points from its 12 games.
The side has scored only 16 goals during the season and conceded 33, including five in a disastrous 10-minute spell last weekend.
Southern United plays Wellington at Forsyth Barr Stadium on Sunday.
