Benfica winger Prestianni denies 'ugly' racism claims
The 20-year-old Argentinian was accused of making a racist insult towards the Brazilian in February, while covering his mouth with his shirt.
The referee stopped the match for 10 minutes and the player was subsequently suspended for the second leg by UEFA, which opened an investigation.
If UEFA finds he abused Vinicius then he will be banned for at least 10 matches.
Real Madrid progressed 3-1 on aggregate to reach the Champions League last 16.
Prestianni told Argentine broadcaster Telefe that...