Atletico Madrid and France striker Antoine Griezmann delivered on his threat and failed to show up for the club's pre-season gathering on Sunday, a club spokesman told AFP.
"Griezmann had an official summons to be at the club at 20.30 this Sunday and when he did not present himself, we opened a file and will study the case," said the spokesman.
Griezmann, a Barcelona target, had already said he would not turn up, Madrid sports daily Marca reported on Saturday, with Atletico then telling AFP that "it changes nothing".
"He us under contract with our club until 2023 and must resume training tomorrow like all the other players," they added.
On Sunday evening, the club tweeted pictures of players arriving at Los Angeles de San Rafael where Atletico traditionally hold their pre-season training, including recent record signing Joao Felix, a teenage Portuguese striker.
Griezmann announced in May that he would be leaving Atletico but could not reveal his destination until his release clause dropped from 200 million euros ($225 million) to 120 million euros on July 1.
On Friday, Atletico accused Barcelona and Griezmann of a "lack of respect" after the Catalan giants' president Josep Maria Bartomeu revealed that the two clubs had held talks about the France international.
Atletico confirmed that they had held a meeting on Thursday, at Barca's behest, to discuss a deal for World Cup winner Griezmann at the lower price.
They also said Griezmann had told them he struck a deal with Barcelona in March.
Griezmann joined Atletico from Real Sociedad in 2014 and has scored 133 goals in 257 appearances.