The Spanish striker never seems to be far away from controversy and his combative and aggressive style of play has split opinion since his arrival at Stamford Bridge.
However, there can be no questioning of his importance to the west London side, with Costa having already scored 15 goals and making five assists in the Premier League so far this season.
Costa was reported to have had a bust-up with manager Antonio Conte earlier this season in various reports in the British media.
But Willian has played down the furore surrounding Costa at Chelsea and has insisted that he is only focused on giving his all for the Blues.
Speaking to Globoesporte, Willian said: “The temperament of the two [Costa and Conte] is a bit difficult, but they are very good people.
“For those who do not know, Diego Costa seems like a tough guy, who wants to fight, but that’s on the field.
“He always tells us, ‘I’m like that on the field, I can not change. If I were to play against my mother, that would be the way I would be’.
“So, he’s a guy who wants to win, he wants to fight, he fights all the balls, he wants to score, and that’s cool.
“Off the field he is a guy who is always joking and talks to us. There is no problem between the two (Conte and Costa).”
Chelsea are currently gearing up for their crunch Premier League clash against Burnley on Sunday afternoon.
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