A childhood friend of Diego Costa has claimed that the striker has "been training with a fitness coach from Atlético Madrid for 40 days" ahead of his return to the Spanish club in January.
It was confirmed last week that the forward had completed his exit from Chelsea, and he was in attendance at Atletico's new Wanda Metropolitano stadium for Saturday's 2-0 win over Sevilla.
But Costa will be unable to feature until January, leading to concerns over his fitness following his lack of first team football since the end of last season.
Costa's friend Valmir Monteiro, however, has revealed that the Spain international has been keeping himself in shape ahead of his comeback.
"Diego Costa has been here with a physical trainer at Atletico Madrid for 40 days," Monteiro said, quoted by Cadena SER.
And he added that Costa "was sure he would return to Spain".
The 28-year-old's move is subject to completion of a medical, but upon his arrival in Madrid he expressed some regret over the circumstances of his Chelsea departure.
"I'm not going to be ungrateful to Chelsea, where I was also very happy, playing in a team that was great," said Costa, quoted by BBC Sport. "Atletico is my home."
He added: "It's not the way I wanted to leave, ever. I have special affection for the people at Chelsea. I'm not a person who is going to smear the image. They know the person I am."
Costa scored 58 goals in 120 appearances for the Blues, and was part of two Premier League title-winning sides during his time at Stamford Bridge.