The Norwegian could be seen mouthing along to the words in a bizarre moment, catching the attention of supporters.
Fans were were quick to take to social media to discuss Haaland's singing.
One Twitter user wrote: "Did I just see Haaland singing the national anthem?"
Another added: "Was Haaland singing the national anthem? Get him in Gareth!"
While a third wrote: "Should have picked England!"
Haaland was born in Leeds before moving to Norway, so his understanding of the anthem is perhaps not so surprising.