Diego da Silva Costa is said to have handed in a transfer request in a bid to force through a move away from Chelsea.
It has been reported that the Spain international is keen to return to Atletico Madrid.
The 27-year-old scored 16 goals for Chelsea last season, but it was a disappointing campaign overall as the West London outfit failed to defend their title and fell to 10th in the standings.
Costa made a quick impression when he moved to Stamford Bridge from Atletico in 2014 by scoring 21 goals in 37 matches, but it is understood that the striker wants to move back to Spain.
According to Mundo Deportivo and Cuatro, Costa is attempting to force his way out by submitting a transfer request.
Doubts over the Brazilian-born's position in the team arose even further when the club signed Michy Batshuayi from Marseille earlier this month.
