The winger missed the squad's final home training session in Portugal on Saturday after falling while attempting an acrobatic shot and causing a traumatism in his shoulder.
He is due to be re-examined before the warm-up match against Mozambique on Tuesday.
"I feel better already," Nani told reporters during the flight from Lisbon to Johannesburg.
On playing in the friendly, he said: "I really don't know, now we have to see. When we get there we'll have to check again."
The other main injury concern in the Portuguese squad is Pepe, who has been recovering from a knee injury he sustained in December.
He has not played since but was last week cleared by doctors from the national side and his club Real Madrid to travel to the finals.
The Brazil-born defender signalled he could already be an option for coach Carlos Queiroz against Mozambique.
"I'm in the group. I'm here to help and now the matter is in the coach's hands," Pepe said as he boarded the plane.
Portugal play their first tournament match on June 15 against the Ivory Coast in Group G, which also includes Brazil and North Korea.
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