Doyen Sports, an investment company, own 75 per cent of Rojo's playing rights. They are desperate for Sporting to accept Manchester United's offer for the Argentina international, but the Portuguese club are holding firm.
Doyen have released a statement complaining that Sporting are "making mindless demands as a condition of 'releasing' the player."
And the company wants Sporting to pay them regardless of whether they accept the offer from United as compensation for the delay.
The statement goes on to say that "if Sporting refuse to sell to United for the €20m offered, the Portuguese club will be contractually bound to pay Doyen 75 per cent of the value of the rejected bid. That €15m would have to be paid within a fortnight."
But Sporting, who have seen off interest from Southampton and Liverpool in the defender, are keen to keep Rojo at the club if possible. They have responded to Doyen's statement on their Facebook page, saying that their agreement with Doyen is terminated "with just cause."
The Daily Express now reports that the ensuing legal battle could take a significant amount of time to sort out. But United have just two weeks left to seal the transfer before the September 2 deadline.
Rojo, a target before Liverpool agreed a deal for Alberto Moreno, has been identified by Louis Van Gaal as the perfect player to play in two of his formation's key positions. The versatile defender can play at centre-back or at left-back, and Van Gaal believes he could play as one of the three centre-halfs, or as a wing-back in United's 3-5-2 set-up.