A friendly between Manchester United and Leeds United at Optus Stadium on Wednesday night has been marred by a series of ugly incidents, including a brawl and a pant-less pitch invader.

The match was supposed to be the pinnacle in a $35 million tourism coup that lured Manchester United to Perth for a 10-day tour.

However, a fight between soccer fans in the stands and a pant-less pitch invader with a missed message, were not the image of Perth acting Tourism Minister, Bill Johnston was hoping to project.

"Any unruly behaviour is always disappointing and negativity is disappointing," he told Nine News Perth.