Denmark midfielder William Kvist injured a rib during the World Cup game with Peru and may not play again at the tournament, head coach Age Hareide said.
Denmark edged out Peru 1-0 in teams' first FIFA World Cup match at the Mordovia Arena in Saransk earlier on Saturday.
"Kvist may have broken a rib," Hareide said.
"We'll see what the doctors say. The symptoms point to a broken rib. If so, he cannot play any more matches at the World Cup. But it's not certain yet."
Denmark will next face Australia on Thursday night (AEST) and the Socceroos will be looking for a result after being edged by France 2-1.