Premier League: Manchester United hit visa snag over new signing
The 24-year-old completed a £16m switch from Sporting Lisbon 11 days ago but a criminal investigation means he is yet to obtain the required working visa.
However, United manager Louis van Gaal is confident Rojo will be in his squad for the Premier League match against QPR on 14 September.
It had been reported issues over third-party ownership were behind the delay.
But the Football Association has already issued his international transfer certificate and has no concerns over ownership issues.
Rojo entered the UK to complete his move to United on a tourist visa.
Immigration laws require that those entering the country to work do so with a working visa. Rojo is currently in Madrid awaiting an interview with embassy staff to secure the document. Officials will examine details of the alleged altercation with a neighbour in 2010 before issuing the working visa.