Atletico Madrid left-back Filipe Luis has claimed that Diego Costa has been training like an "animal".
The striker returned to the Spanish club in a £58m deal from Chelsea in the summer after falling out of favour under manager Antonio Conte.
Costa has been unable to play for Diego Simeone competitively as he cannot be registered until January due to the club's transfer embargo.
"It is frustrating seeing him playing like an animal [in training], but he can't play," ESPN quotes Luis as saying. "It's just a month until he can play with us. He'll help us a lot. I don't have any doubts about it. He knows the club, he knows the way we play.
"He has already adapted. I know it was difficult times for him and for Chelsea. Now everybody's happy. We want to see him play and happy again.
"I think he came back to Atletico because Chelsea couldn't keep him because it's his desire. He really wanted to come back to Atletico. He was happy here. He did his job really well. His most important desire was to come back."
Costa spent four years at Atletico before signing for Chelsea in 2014, where he won two Premier League titles and the EFL Cup.
