Arsenal captain Laurent Koscielny has refused to travel on the club's pre-season tour of the US.
The 33-year-old France defender is out of contract at the end of the 2019-20 season and is a reported target for French clubs Bordeaux, Rennes and Lyon.
"We are very disappointed by Laurent's actions, which are against our clear instructions," said Arsenal.
"We hope to resolve this matter and will not be providing any further comment at this time."
Bordeaux have reportedly offered Koscielny a three-year deal.
The central defender joined Arsenal in the summer of 2010 for a fee of around £10m.
A frustration that had been brewing for some time - analysis
BBC Sport's David Ornstein
Towards the end of last season, Arsenal and Koscielny were in negotiations over a contract extension - most likely for an additional year on top of his remaining 12 months.
The conversation was progressing positively but then Arsenal were beaten by Chelsea in the Europa League final, a result that has had major repercussions for the Gunners.
As well as causing significant damage to their recruitment plans and possibilities, it also changed certain situations regarding existing players and none more so than Koscielny.
The 33-year-old is understood to have become increasingly discontent since his return in December from an Achilles injury, primarily over the management of his playing schedule and the direction in which he feels the team and club are moving.
While Koscielny was optimistic that Champions League qualification could lead to a better future for both parties - hence the contract talks - missing out exacerbated his misgivings and led him to decide the time had come to move back to France.
On returning from a summer break and with firm interest from clubs in his homeland, Koscielny informed Arsenal of his wish to leave and hoped his nine years of service and professionalism until this point would help achieve an amicable resolution.
However, Arsenal rejected the request and made it clear that they need and expect the Frenchman to honour his contract and be a key part of their squad in the coming campaign.
Given that head coach Unai Emery was happy with Koscielny's performance in 2018-19 and already faces other issues in central defence, the view was that he could only go if a bid landed that reflected his value and importance to Arsenal.
Koscielny argues that Arsenal are reneging on an agreement that would allow him exit as a free agent during the current transfer window, something the Gunners strenuously deny.
He is also thinks Arsenal have - or will receive - an "acceptable" offer, but some privy to the proposal admit that "acceptable" is subjective and others insist there is nothing on table.
When Koscielny told Emery in a face-to-face meeting on Wednesday morning that he would not be joining the team on their pre-season tour to the USA, the Spaniard was furious.
Arsenal's head of football Raul Sanllehi later sent Koscielny a message expressing bitter disappointment and warning the player that not travelling would be in breach of contract.
Koscielny replied emphasising his stance and on arrival at Arsenal's London Colney training ground on Thursday morning the captain confirmed he would not be boarding the flight.
He will be required to train alongside the players who are not on the America trip - mainly youngsters - with disciplinary proceedings under way to determine his punishment.
Arsenal officials are fuming about the situation, which from a sporting perspective gives them a headache in central defence - an area they were already looking to strengthen this window.
They were thought to be close to completing the 30m euros signing of William Saliba from Saint-Etienne, with plans to loan the 18-year-old back to the Ligue 1 side for the entirety of next season.
But in a dramatic twist on Friday, Tottenham reignited their interest in Saliba and were pushing hard to complete the transfer from under the noses of Arsenal.
Meanwhile, Rob Holding is recovering from a knee injury and there are concerns over the development and readiness of Konstantinos Mavropanos to provide a credible option.
Arsenal are keen to sell Shkodran Mustafi but the German is under contract until 2021 and has no desire to depart.