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By Mike Hedge

MELBOURNE, Aug 22 AAP - A senior police officer says he sat frozen in shock as jockey Danny Nikolic stood toe-to-toe abusing one of his colleagues in a Melbourne police station.

Nikolic is charged with assaulting Detective Senior Constable Julio Salerno following an official interview at St Kilda police station in March 2011.

Sergeant Dave Eadie told the Melbourne Magistrates Court Nikolic had participated willingly in the interview but became agitated after having a short conversation with Det Sen Const Salerno after the recording devices were switched off.

"Nikolic said he wasn't happy with Julio Salerno being present," Sgt Eadie told the court.

"He told him `get the f*** out of here, I'm not speaking with you'."

Sgt Eadie said the two men stood up and their foreheads were touching and Nikolic was red in the face.

Det Sen Const Salerno pushed Nikolic back into his chair but the jockey immediately bounced back to his feet and continued the confrontation.

The court heard they again stood with their foreheads touching with Nikolic goading the officer urging him to "have a go".

"I sat there and froze, it was behaviour that shocked me," Sgt Eadie said.

Nikolic had come to the police station to be questioned about other matters, including an alleged assault on fellow jockey Mark Pegus with which he was duly charged.

Both assault charges are being heard by Magistrate Angela Bolger.

Pegus claims Nikolic, who is banned from riding after making threats against Victoria's chief racing steward, assaulted him at the Caulfield stables of trainer Byron Cozamanis in January 2011.

But he says he only reported the incident after Nikolic allegedly assaulted his girlfriend two months later.

Pegus told the court an altercation between the two began with a phone call in which Nikolic accused him of spreading rumours about his brother. It continued the next morning when the two arrived at the stable to ride trackwork.

In the belief that they were going to discuss their differences, Pegus said he followed Nikolic into the stable office where things turned violent.

"As I walked in Danny flew at me and started throwing punches," he told the court.

Det Sen Const Salerno is due to give evidence in the contested hearing on Friday.