Rio 2016 organisers have confirmed that a controlled explosion was carried out at the basketball venue before Spain and Nigeria's pool match.
Security has been tightened after a bus carrying media representatives was pelted with stones, while bullets have flown through the equestrian venue - situated inside an army base.
A similar explosion was carried out on a bag near the finish of the cycling road race, with officials confirming that the suspect bag at the Carioca Arena was non-threatening.
The organising committee's statement read: "A routine inspection in Carioca Arena 1 found an abandoned backpack just before the men's basketball match between the teams of Nigeria and Spain.
"Following safety protocols, the public was held on the outside of the arena while experts were preparing to remove the object.
"A preliminary examination of the location and size of the backpack allowed the experts to authorise the start of the match and the presence of journalists in the stadium. Only the public were kept outside because the place where the bag was found was next to a spectator passageway.
"The backpack was near a trash container in the bathroom on the top floor. A controlled explosion following the guidance of the Federal Police and the Army was undertaken.
"Inside the bag were found a tablet, a pair of socks and a jacket. Immediately after the detonation the public were allowed to enter."
Spain star Pau Gasol, who helped his team to a 96-87 victory, said players were confused about the situation.
"We heard the explosion. We didn't know exactly what it was. We just kind of looked around and said, 'What's going on? What's happening here?' We didn't know," he said
"We thought maybe nobody came to watch the game. At first, we just heard the noise and looked around but we saw everything was OK."