Di Francesco denies Costa racism allegations

Costa was sent off for aiming an elbow and headbutt before spitting in the face of Di Francesco, the son of Roma coach Eusebio Di Francesco, in Sunday's game the champions won 2-1 in Turin thanks to Cristiano Ronaldo's first goals for the club.

Costa, 28, later posted an apology to his teammates and fans on his Instagram account, although he replied to one comment by saying that people did not know what Di Francesco had said to him.

"You don't know what he said to me. But no big deal... I say sorry to all those who I have to say it to, because I did wrong," Costa wrote.

And amid the speculation, 24-year-old Di Francesco hit back at suggestions he had aimed racist insults at his rival.

"I'm deeply troubled by the allegations and inventions that have appeared in some national media outlets," Di Francesco said on Sassuolo's Twitter account.

"All of this is offensive and derogatory. I won't allow any racist behaviour and/or phrases, which do not belong to my ethical values and are the fruit of other people's imagination, to be attributed to me. I ask for and demand respect!"

Costa faces a lengthy ban and a hefty fine from his club, with Juventus coach Massimiliano Allegri furious with the player for "rising to provocation".