Mortimer is reportedly good friends with a member of the Zuma family, and claims Pistorius said "My family owns SANDF [South African National Defense Force]. Zuma works for us. I'll [expletive] on Zuma."
"We can confirm that Oscar was at a night club with one of his cousins," according to a Pistorius spokesperson.
"They sat in a quiet area of the private VIP section when they were approached by the individual you have identified as Mr. Mortimer. The individual in question, according to our client, started to aggressively engage him on matters relating to the trial. An argument ensued during which our client asked to be left alone. Oscar left soon thereafter with his cousin. Our client regrets his decision to go into a public place and thereby inviting unwelcome attention."
It's unclear, but there may have been a brief scuffle before Pistorius left the club.
But club manager Perry Mermigas insisted to the Daily Mirror there was no altercation, and that he walked his VIP guest out of the club himself.
"That's why I was very surprised with these stories. It was the first time he had been to our club. I just welcomed him then thanked him for coming as he left. I think people are just trying to put a story out there because the case is ongoing."
The 27-year-old athlete is accused of killing his model girlfriend Reeva Steenkamp during an incident at his home on Valentine's Day in 2013. Pistorius claims he mistook the 29-year-old for an intruder, but prosecutors say he murdered her.
The murder case was adjourned until Aug. 7 to give both legal teams extra time to finalize their final arguments. If convicted, Pistorius could be sentenced to life in prison.