Angel di Maria has said that Manchester United will have to keep a "close eye" on Alexis Sanchez during their FA Cup quarter-final tie against Arsenal.
The former Real Madrid winger will come up against his old Barcelona rival for the second time since their summer moves to the Premier League when the Gunners travel to Old Trafford on Monday.
The Argentina international told Man Utd's website: "Sanchez is a player who has been in some great form this season and since he came to Arsenal he hasn't stopped scoring or creating goals.
"He's been tremendous and seems to be the key player for Arsenal. When he plays well, they seem to play well too. We've seen him in various games.
"If he gets hold of the ball and does what he can with it, then that works well for Arsenal. We have to keep a close eye on him and try to prevent him from creating openings with his passing as we know that every time he gets to run at you he can create danger."
The winner of Monday's match will play at Wembley in the semi-finals.