The Tottenham attacker left the field with an ankle problem in the 41st minute of the all-Scandinavian encounter, with the Danes one goal to the good thanks to a William Kvist strike.
Nicolai Boilesen snatched victory for Morten Olsen's men at the death, after Marcus Pedersen had pulled Norway level, but post-match thoughts were with the stricken Eriksen.
"We don't know if he's out for four or six weeks or how long it will take," Olsen said. "It's bad for him at a new club."
Eriksen has made 12 appearances in all competitions for Tottenham since arriving from Ajax in the close season.
The injury could rule him out of important fixtures against Manchester City (November 24) and Manchester United (December 1) in the Premier League, as Andre Villas-Boas' men look to improve on their current position of seventh.
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