The Daily Mail says it is understood Van Gaal is growing increasingly irritated by United's failure to land targets and last week saw interest in Belgium defender Thomas Vermaelen come to nothing when the 28-year-old moved from Arsenal to Barcelona.
Despite third party ownership complications for Sporting, United remain in the hunt for Rojo.
United were refusing to comment publicly on the matter but it is understood their interest in the player remains active. Indeed, they have not ruled out movement on the issue over the weekend.
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