Norwegian media has been in frenzy over the news, especially since the team lost to Denmark 2-0 only four days later, marginalizing its chances to qualify for Euro 2012.
In an interview with national news agency NTB, Riise said he had phoned Olsen and apologized for coming back late to the hotel after Norway's 1-0 victory against Iceland.
Riise, who didn't play himself because of an injury, admitted there had been "alcohol on the table. We had fun and unfortunately I forgot the time," but underscored that he consumed only limited amounts and that no one was drunk.
"I drink very, very seldom, perhaps two-three times a year," Riise said.
Mari Waagard Thomassen, a spokeswoman for the Football Association of Norway, confirmed the defender had been in telephone contact with Olsen on Friday "to explain himself," but could not go into more detail.
According to Norwegian daily Dagbladet, most of the players returned to their hotel around midnight, but Riise and some of the others came back hours later.
It also cited Olsen as having said that several of the players underperformed during Tuesday's game against Denmark.
Norway's only remaining game is at home against Cyprus.