South Sudan's Nuni Omot has apologised for the incident, though match officials saw no foul play.
"After Simanic was operated on for the first time in the night between August 30 and 31, the doctors monitored the postoperative recovery and decided that due to complications, a new operation (on September 3) was necessary," the federation said in a statement.
Simanic is in a hospital in Manila. The 19th edition of FIBA's flagship event is being co-hosted by the Philippines, Japan, and Indonesia.
Omot, in a statement released by South Sudan's federation, wished Simanic a speedy return to the court.
"As a sportsman, I firsthand understand the severity of his situation and I am deeply sorry that this happened," he said. "No player should have to go through that."
