Amorim joins Portugal injury list
"A scan has confirmed the injury. A period of six days of complete rest is expected, with treatment and a gradual integration of training sessions from next week," the Portuguese Football Federation said in a statement on Tuesday.
The federation added Amorim picked up the injury in training before Portugal's 7-0 thrashing of North Korea on Monday.
He will miss Friday's Group G match with Brazil in Durban.
The versatile 25-year-old, who prefers to play in central midfield but was used mainly as a right-back in Benfica's title-winning season, won his first cap in the 0-0 draw with the Ivory Coast last week, coming off the bench after 85 minutes.
The federation added that midfielder Deco, who was ruled out of the North Korea game with a hip injury, is still receiving treated and is training separately from his team-mates.