Louis van Gaal believes there is plenty more to come from Anthony Martial – but warned Manchester United fans he will not always be as scintillating as he has been in his first three games.

The 19-year-old moved to Old Trafford on transfer deadline day, becoming the most expensive teenager in world football as he joined from Monaco for an eye-watering £36 million (Dh205m).

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But after scoring on his debut against Liverpool, he bagged a brace on his full Premier League bow as United won 3-2 at Southampton to move second in the table.

Graziano Pelle had given Saints the lead before Martial struck either side of half-time to turn the game on its head – Juan Mata adding the third and Pelle planting a late header as a consolation.

David De Gea, who almost departed United 24 hours before Martial arrived, was on hand to make two fine saves but it was Martial who had Van Gaal purring afterwards. “He needs to adapt to the English culture, he is doing great – three matches in a row and three goals,” the Dutchman said of his new forward.

“He cannot speak English, I speak French with him. I need help with that from Marouane Fellaini and Morgan Schneiderlin, it is very difficult but he is willing to speak English.”

“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. He can improve I think but he has a high level of talent. He shows it.”