The French striker did not play a part as the Red Devils comfortably booked their place in the last 16 of the Europa League after suffering the problem.
Martial is a now a doubt for Manchester United’s Premier League showdown with Arsenal at Old Trafford on Sunday afternoon.
However, Van Gaal insisted that the injury is not too serious and he missed the game against the Danish champions as more of a precaution.
Speaking to BT Sport after the game, Van Gaal said: “It should be his first muscle injury [since arriving at the club].
“But he is smart and wise to step out. It is not a rupture or anything like that. A tight hamstring. I don’t think it is very heavy.”
The Manchester United manager then continued his assessment of the injury situation in his post-match news conference at Old Trafford.
He continued: “Anthony can be tired. He’s only 20 and he’s played all the matches so it’s not so remarkable. He stepped down himself and that I like very much.
“I have already explained to you the only muscle injury we have is Marouane Fellaini. That we know already when he played so many matches in a row.
“It’s always like that when you don’t have other players and it’s difficult to change or rotate. So the next muscle injury would be [expected to be] Martial but I don’t think he has a muscle injury. He is very intelligent – he steps down when his hamstring is tight.
“You have to cope with that, it’s difficult also for the team because, after David De Gea, now Martial, and Martial and De Gea have played very good seasons, I think, and they have to be replaced.”
United head into Sunday’s clash with Arsenal in fifth place in the table and six points behind the top four.
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