The Real Madrid winger strained the back of his right thigh in Argentina's 1-0 win over Belgium, and was to undergo medical tests today to discover the extent of the injury.
Losing Di Maria would be a big blow for Argentina as it prepares for its first World Cup semifinal since 1990. Besides Lionel Messi, he's been Argentina's most influential player in Brazil.
Di Maria scored the extra-time winner against Switzerland in the second round and set up Gonzalo Higuain's winning goal in the first half against Belgium yesterday.
Coach Alejandro Sabella called Di Maria "vital" to Argentina, which is already missing striker Sergio Aguero due to injury.
Sabella also praised Messi's performance against Belgium, even though he didn't score. The four-time world player of the year started the move that resulted in Higuain's goal, pirouetting past two Belgium players before giving the ball to Di Maria whose pass deflected off a defender into Higuain's path.