Jonas was detained on Sunday for allegedly sexually assaulting a female room cleaner, police say.
A Namibian boxer arrested for alleged sexual assault at the Rio Olympics athletes village lost his opening bout on Thursday and is out of the Games.
Jonas Junias Jonas, 22, was released just hours before losing a unanimous points decision to Frenchman Hassan Amzile.
Jonas was detained on Sunday for allegedly sexually assaulting a female room cleaner, police say. It was the second sex assault case to rock the Games village.
The light welterweight refused to answer an questions from reporters on his way back to the dressing room after his defeat. Several stony-faced officials surrounded him.
International Olympic Committee spokesman Mark Adams earlier said that Jonas, who carried the Namibian flag at the Olympics opening ceremony, had been released "pending further investigation".
In a separate, but similar incident at the athletes village, police arrested Moroccan boxer Hassan Saada, also 22, on suspicion of sexually assaulting two female cleaners.
Rio organising committee spokesman Mario Andrada said prior to the Jonas fight: "I understood that both boxers have been released this morning. That doesn't mean that the legal process is over but I understood that they have been released and one of them (Jonas) is able to compete.”
Saada is also out of the Games after his fight on Saturday was ruled a walkover.