Marcos Rojo will not play for Manchester United against Sunderland on Sunday because his work permit has not yet been processed.

The Argentine was today unveiled by manager Louis van Gaal at a press conference but told the club's inhouse tv station MUTV that the 24-year-old would have to wait to make his United debut.

Under United Kingdom rules, any player who is 16-years-old or older and is not from the European Economic Area requires a work permit to play for a British club.

Rojo has been training with his new team-mates this week but the lack of a permit means United will again be without a left-footed centre-back for their Premier League match against the Black Cats on Sunday.

There has also been mixed injury news for Van Gaal after it was revealed new signing Ander Herrera had been sidelined.

The £29m signing from Athletic Bilbao started in United's midfield in their 2-1 defeat to Swansea but was replaced by Marouane Fellaini in the second-half.

Van Gaal did not divulge the nature of the injury or how long the Spaniard will be out for, but the 25-year-old becomes United's fourth midfielder to be ruled out.

"We have seven injuries," Van Gaal confirmed. "I have never had this as a manager, it is the first time."

He was however boosted by the return to full fitness of Robin van Persie, who is expected to start at the Stadium of Light on Sunday.

"Robin is ready to play so that is a big benefit for our team. I am happy he can play," Van Gaal added.

United's missing midfielders are Herrera, Marouane Fellaini, Michael Carrick and Jesse Lingard.