New South Wales Labor MP Paul Gibson says he was thrown against a car and bashed in the car park of a McDonald's restaurant in Sydney's north-west on Saturday afternoon.

Mr Gibson has told Macquarie Radio the American attacker king-hit him around 3:00pm on Saturday and repeatedly yelled, "This is how we do it in America," as he smashed his head against the gutter.

The Blacktown MP said he was told by a witness the man had a pistol in his coat and an ID that showed he was a US secret agent, but police have been unable to confirm the claim about the gun with witnesses.

Mr Gibson told Macquarie Radio the argument started when he was trying to park beside the man and "gave him a friendly toot" to close his car doors.

He said the man got out of his car and waved him in, before accusing him of running over his foot.

"I said, 'I couldn't have run over your foot... I was a long way away from your foot,'" he said.

"But I said, 'If I did, I'm sorry,' and I said, 'Is it OK?' He said, 'Yeah, it's fine'.

"I proceeded to walk into McDonalds and the next thing I knew, I thought I was in la-la land and I looked up and I could see the sky and I didn't know what happened.

"Apparently, what he's done, he's came, he's king-hit me in the back. I've just had neck and back surgery over the last couple of years and a knee replacement.

"And he's thrown me up in the air, speared me into a bonnet of a four-wheel drive apparently, then he's got me again, had his head between my legs and he's speared me into the road.

"Then he's proceeded to jump on top and pound me in the head and what have you and they tell me he was just getting my head and he was just smashing it into the gutter."

"I've done an AC joint in my shoulder and I've done some ribs, I think, and I've got some trouble under the ribs and I'm passing a bit of blood and what have you."

Police said Mr Gibson suffered abrasions and bruising to his shoulders and ribs.

The attacker has been described as African American and about 185 centimetres tall, with a crew-cut hair style, acne scarring and solid build.

He was wearing dark clothing at the time.

Police want anyone who might know the man's identity to call Crime Stoppers on 1800 333 000.

Mr Gibson has been the subject of assault allegations himself.

Last year, he was investigated over claims he assaulted a man who had threatened him in Blacktown.

In 2007, he was stood down from Cabinet just hours after being sworn in because of claims he had assaulted his partner. He was later cleared of the allegations.