Detective Superintendent Brett Guerin urged fellow Bandidos members not to retaliate, saying it was the police job to enforce the law.
A former champion heavyweight kickboxer, Mitchell is said to be in a relationship with Danielle McGuire, ex-partner of Tony Mokbel, the former drugs kingpin extradited from Greece in 2008. As well as McGuire, police intend to speak to Roberta Williams, widow of the murdered gangland figure Carl Williams.
Although the attempt on Mitchell's life has sparked fears of a revival of the city's underworld wars, Guerin said it was "spectacularly unsuccessful".
"In terms of professionalism, compared to some of the murders that we have seen in Victoria over the past five or 10 years ... I wouldn't call it professional."
After being attacked outside Doherty's Gym, Michell staggered across the carpark, pursued by the gunmen. He was wounded in the hip and back.
Shoppers flung themselves to the ground when shots began flying at about 4.30pm.
The gunmen, who were armed with high-powered, semi-automatic pistols, sped off after the shooting.
Mitchell, who is under police guard in hospital, is refusing to co-operate with detectives. He was a suspect in the 2003 gangland execution of a drug dealer, Mark Malia, whose charred remains were found in a wheelie bin dumped in a stormwater drain. Carl Williams eventually pleaded guilty to the murder.