Louis Van Gaal admits he faces a battle to manage the expectations growing around Anthony Martial after the striker took his tally to three goals in his first three Manchester United games.

Martial followed his debut goal against Liverpool with a double in the 3-2 victory at Southampton that moved United up to second place in the Premier League table on Sunday.

The forward arrived at Old Trafford following a £36 million (49.6 million euros) move from Monaco at the end of the transfer window.

Yet while there were doubts expressed about the size of the price-tag, Martial has wasted no time making an impact.

"Anthony Martial is already special because we paid a lot of money for him. A lot of people are thinking he is a great star but he is a boy of 19. In three matches he has shown a lot," said United boss Van Gaal.

"I am very happy with him but we and he have to keep our feet on the ground."

Van Gaal admitted the youngster will need time to settle into his new surroundings.

"He cannot speak English, I speak French with him, I need help with that with Marouane Fellaini and Morgan Schneiderlin, it is very difficult but he is willing to speak English, it is a matter of time but when he speaks English good enough he will answer the questions.

"First he needs to adapt to the English culture, he is doing great -- three matches in a row and three goals.

"He has the talent for it. When you are 19 years old you cannot expect consistency. Emotionally they shall have a lot of dips so that I expect also from him but that is not a big problem for me.

"I'm very happy that he is in three matches and his talent is at a high level and he adapts to the system of how we want to play, that is also important, not every player can adapt in that system but he shows he wants to do that and he can do that.

"He scores goals. That is the most important thing, that as a striker he scores goals.

"That is his quality, his talent. He can improve I think but he has a high level of talent. He shows it. He shows it under great pressure and that is maybe his greatest talent."

Martial scored twice after Graziano Pelle had put Southampton ahead with Juan Mata adding United's third before Pelle headed a late second.

A mistake from Maya Yoshida led to Martial's second and Southampton manager Ronald Koeman said: "I hate always players, in general not criticising Maya, I hate players who pass the ball always back to the goalkeeper, play it into the space in front."

He added: "There were several moments in the game where you put the pressure on them. We saw the weaknesses of Manchester Untied today, defensively."

But Van Gaal took issue with the suggestion United were flawed at the back.

"Have you seen the goal average against, also last season. All the media was writing the defence is very bad but at the end we were third in the Premier League."

Responding to Koeman's claim that United displayed defensive weaknesses, he added: "This is also remarkable, that he says that."