True, but I imagine with good performances he will see a lot of time in midfield, or potentially as a centre-back if we don't sign anyone to partner Smalling. I'll be surprised to see Mourinho keep Blind as first choice centre-back. That said, unless he is a starter, he will be able to cover at RB most times. I think he's better as a LB, CM or CB, though.
Varela is another option. I'd like to see us not sign a new RB just so that we can have Varela show what he can do, with him and Valencia being our two main options there. I think he can be a big player for us. He goes forward like a Manchester United full-back should, but he also knows how to defend one on one.