Koscielny, 33, is now facing disciplinary action and being stripped of the captaincy after refusing to fly with the rest of the Arsenal squad to the United States.
But Mirror Sport can reveal the background to the fall-out is that Koscielny has had a three year contract offer from Bordeaux and is also upset at what he sees as being made to take a “substantial” pay cut by Arsenal.
France defender Koscielny has one year left on his current £120,000-a-week deal, wanted an extension and had held discussions with the club about getting an extra 12 months.
Arsenal were willing to give Koscielny a new two year deal but because of his injury record they offered a lower basic salary which included performance-related pay based on appearances and the option for a free transfer next summer.
They also insist he could have ended up earning more with the extension than on his current deal with bonuses especially if Arsenal had got back into the Champions League.
But Koscielny rejected the offer, has been left fuming and believes the club should allow him to leave for free now to take up the chance to go home to France with Bordeaux offering a three year deal and that is why he is so upset with Arsenal.
Mirror Sport understands the row has been brewing for some weeks and reached boiling point on Monday when Koscielny turned up and made it clear he did not want to train.
Koscielny has ended up training this week but Arsenal feared the stand-off was coming on Wednesday and their club captain reported today but said he did not want to go to the United States.
It is hard to see a way back for Koscielny as, even with the background to the flare-up, fans are unlikely to forgive his actions as he was under contract and the club captain supposed to be setting an example.
Arsenal do not want to grant the 33-year-old a free transfer and are now making him report up every day, train with the under-23s while the club are in the United States. Koscielny is certain to face more action including a club fine while Granit Xhaka is favourite to get the armband.
Arsenal took the unusual step of issuing a club statement to go on the front foot and it read: “We are very disappointed by Laurent’s actions, which are against our clear instructions. We hope to resolve this matter and will not be providing any further comment at this time.”
It is a major headache for Arsenal who are already short defensively and now their captain seems certain to leave after nine years at the club.
Arsenal have already signed St Etienne youngster William Saliba but will loan him back for next season and Rob Holding could miss the start of the season as he battles back from a knee injury.
They already wanted another senior centre half even before the Koscielny row and now this will only intensify the search although it could also offer the chance for Konstantinos Mavropanos or Calum Chambers to step up.