Louis van Gaal’s frustrations in the transfer market have reached new heights after his pursuit of Argentina defender Marcos Rojo was stalled by a row between the 24-year-old’s agent and his club Sporting Lisbon.

With the Barclays Premier League season due to start when United host Swansea at Old Trafford tomorrow lunchtime, the club have now not signed a player since they spent more than £50million on Luke Shaw and Ander Herrera in the last week of June.

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.

Now Van Gaal and United chief executive Ed Woodward are facing obstacles as they attempt to sign Rojo after Sporting became embroiled in a bitter public row with the Doyen agency that represents the player.

With Doyen owning 75 per cent of the South American, Sporting are understandably keen for any potential buyer to meet a release clause of £24m. United have so far offered £16m but Sporting have accused Doyen of encouraging interest from the English club and of sending an employee to a meeting with them pretending to be an Old Trafford director.

United were last night 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.– Daily Mail