Paralympic star Oscar Pistorius will not be prosecuted on an assault charge, Pretoria police said on Tuesday.

"The director of public prosecutions looked at the docket and read all the statements and doctors' reports and decided that the State did not have enough evidence for a successful prosecution," said Inspector Marinda Stoltz.

"He also found that there was no intention to assault."

Pistorius (22) spent a night in September behind bars for allegedly assaulting a woman who had attended a gathering at his Silverlakes house.

The 19-year-old, a friend of his, was allegedly fighting with her boyfriend during a small get-together.

Pistorius told them to go outside. She later returned to the house alone and allegedly started kicking the doors.

While she was doing this Pistorius opened the door and told her to leave his house. When he closed the door on her, one of the door panels allegedly hit her on the leg.

Pistorius was charged with assault with the intent to cause grievous bodily harm. He was released on a warning after the charge was changed to common assault.