The 28-year-old Frenchman moved to Old Trafford for around £34m, leaving Real Madrid after 10 years with the Spanish giants.
Fernandes has been impressed with Varane's immediate impact with the Red Devils and believes his winning mentality will benefit the rest of the squad.
"[Varane is] a winner. Everyone knows that. He's a nice guy and works really hard and is always pushing everyone to do better. I think he has a great mentality," Fernandes told The Mirror.
"Rapha has been brilliant. [He] is really important for us. In football, we all have different qualities, and Rapha has different qualities to Victor [Lindelof], Harry [Maguire], Eric [Bailly] and Phil [Jones], but they can all add different things.
"Still, he's a little bit shy in some ways, because it's the beginning for him at United, but I think he's a leader. I think he can help in that part of the game."
Fernandes, who missed a crucial penalty in United's 1-0 defeat against Aston Villa last weekend, will be hoping to make amends when the Red Devils face Villarreal in the Champions League on Wednesday night. body check tags ::