Louis van Gaal has said that Marcos Rojo must focus on his discipline now that he has completed his move to Manchester United.
The former Sporting Lisbon defender finalised his switch to Old Trafford earlier this week, and was formally unveiled to the media this afternoon.
The manager told reporters: "He has to be aggressive in the right moment. When I have to say something about him that I have to criticise, that is it, he has to control himself in every moment.
"He can improve in that and maybe I can help him. I think Marcos fits into the profile as a left central defender or a left wing-back."
Rojo received 21 yellow cards and was sent off four times in his 49 appearances for the Portuguese side.
