Manchester United manager Louis van Gaal warned on Friday that there is a danger that defender Marcos Rojo's shoulder injury could recur in the future.

Argentina international Rojo dislocated his shoulder in United's 1-0 derby defeat by Manchester City at the Etihad Stadium last weekend.

Rojo, who joined United from Sporting Lisbon in August, is likely to be out for up to six weeks, although more of a worry is the possibility that the injury could happen again.

"Maybe with Rojo's injury, it is very difficult that it shall not happen again and that is the problem," van Gaal told his weekly press conference.

"Marcos dislocated his shoulder, but he did it in the right way. He doesn't need an operation, which is a relief. Yesterday (Thursday) evening, another specialist said that a conservative way to heal it is the best.

"However, it is always a risk it could happen again. I cannot change that. The human body has been made by God, not by me. It could be less than six weeks, but with an operation it would be 12 weeks."

Rojo's absence has added to van Gaal's problems in the heart of defence ahead of the visit of Crystal Palace on Saturday.

Chris Smalling is suspended after he was sent off in the derby against City and Phil Jones is out with shin splints, while Jonny Evans is nursing an ankle injury.

Midfielder Michael Carrick is poised to deputise in central defence alongside either Tyler Blackett or Paddy McNair.

Van Gaal acknowledged that the growing injury list at Old Trafford has hampered the implementation of his football philosophy.

"When I want to select the same line-up, I cannot," said the Dutchman. "You cannot create consistency and that's important in football.

"But I don't want to complain or cry, because I have great belief in not only the players, but the staff and also the supporters who are supporting me."

Van Gaal also admitted United's disappointing start to the season has left him feeling "lousy".

The 20-time English champions currently lie in 10th place in the Premier League with 13 points after 10 matches.

Van Gaal's predecessor David Moyes, who was sacked in April, had 17 points following the same number of games in his brief tenure.

It is also United's worst start to a league campaign since the 1986-87 season, immediately prior to Alex Ferguson's record-breaking 26-and-a-half-year tenure as manager.

"It's not good enough. I feel myself very lousy and for the fans also," van Gaal added.

"Also the board, because they have a great belief in me and my staff. When you have 13 points after 10 matches, you are not doing well.

"We are in the process. When we won every game on tour in the United States, I said that the process shall take more than one year. It can be it takes three years.

"I hope -- because that is always dependable on a lot of aspects -- we shall make it happen that we shall win a lot of matches in a row.

"I have experience that people have great belief in what we are doing now, the way we are playing football. Because when I have been in the streets, I have been surrounded by very positives things.

"The belief is high, but I know of course I am feeling lousy that we only have 13 points out of 10 games."