Canaries boss Chris Hughton said: "It was so innocuous because there was no contact. It is a shame. We know he went over on his ankle. He is being assessed. He will certainly be out for a period of weeks, a month-plus rather than short of that. It is disappointing for us.
"He will be a big loss because he is a young player of fabulous potential. It was a big move for Harry to come here, an exciting move. I feel for him at the moment."
Hughton added: "It is a real disappointment, especially when he was just up and going. He has settled in very well. We just hope it is a shorter period out rather than a longer one."