MANCHESTER -- Marcos Rojo will not be available to make his Manchester United debut against Sunderland on Sunday because his work permit has not been processed.
Manager Louis van Gaal said another new signing, Ander Herrera, has joined a lengthy injury list with fellow midfielders Michael Carrick, Marouane Fellaini and Jesse Lingard also sidelined.
United will go to the Stadium of Light without seven injured players as well as the ineligible Rojo, but Robin van Persie will be available to make his first appearance of the season.
Marcos Rojo is not eligible to play this Sunday vs Sunderland. Van Gaal tells #MUTV he still needs a work permit.- Manchester United (@ManUtd) August 22, 2014
Van Gaal explained his decision to sign the 24-year-old defender -- who joined from Sporting Lisbon for 16 million pounds on Wednesday -- by explaining he can operate either as a wing-back or a left-sided centre-back.
Former Netherlands coach Van Gaal said at a news conference: "I played [against] him in the World Cup so I have to analyse Argentina. I was already enthusiastic about him because my philosophy is you have to buy only players who fit in the profile and I think Marcos fits in the profile as a left central defender but also as a left wing-back.
"He played for Argentina left wing-back but at Sporting Lisbon he played as a left central defender so I think he shall [fit] our profile. He played a fantastic World Cup so I am very pleased."
But Van Gaal warned the Argentina international, who was sent off four times during two seasons in Portugal, that he needs to improve his disciplinary record.
"First of all, he needs a lot of brain to be aware of spaces because we are defending spaces and that is the first word I used to him," he added. "He has to be a very good header because the Premier League is playing with long balls and also his buildup has to be good, and I like the way he played in the World Cup so that is also very important -- he has to be aggressive in the right moments.
"When I have to say something that I have to criticise, maybe that is it -- he has to control himself in every moment and maybe he can improve and I can help him."
Rojo -- who appeared alongside Van Gaal at the news conference -- said: "I am very happy to be here at the biggest club in the world. It is a great honour and I am pleased to be here to bring the best I can to this club."
He added on United's official website: "I know a lot about the club because I always follow the Premier League and Manchester United were always my team because they were the biggest and the best. Juan Sebastian Veron played for United and was a great player and I always watched his progress. United were always my club.
"I always give everything I have in a game and I leave everything out there on the pitch. I play each game as if it could be my last. That's the most important thing in my philosophy.
"I think the most important thing is that I keep growing as a player and keep improving. I have worked really hard for this opportunity and now I am at the biggest club in the world and I want to win trophies."