The two historic rivals are set to face off at Elland Road on Sunday in the Premier League.
Despite playing for rivals, Fernandes and Raphinha are good friends as they played together at Sporting CP.
Fernandes was asked about Raphinha by a United fan from Nigeria, and responded, per the club website: "About Raphinha, unluckily for Leeds, I think maybe he will still be injured at the time.
"I hope not. I hope I can play against him but, if I have to put him down in the game, I will put him down!
"The relationships stay out of the game. He knows that. He is one of the players who knows me better than anyone.
"He knows the relationship but even in the training ground, he knows it never counts when we play against each other.
"If we have to fight in the game, we'll fight for everything and then go home.
"If there is time to see each other, we will see and we will talk but he knows, in the game, there are no friends at all."