Mitchell, 38, sergeant-at-arms for the notorious gang, was ambushed and shot in an arm as he walked into the clubhouse of another outlaw gang at a Melton industrial estate.
Multiple shots were fired and three cars were damaged in the incident in Norton Drive.
A Melton man who was with Mitchell was grazed by bullets.
The shooting happened at the clubhouse of the Diablos, an outlaw gang linked to the Bandidos, about 10pm on Friday.
Investigators are expected to probe whether it was a planned hit on Mitchell, amid suggestions the gunman had been laying in wait for him.
Mitchell, of Point Cook, was taken to the Royal Melbourne Hospital with non-life-threatening injuries. He remained there last night.
The bikie hardman spent months in the same hospital after he was shot five times in November 2011, outside Doherty's Gym in Brunswick. He was on life support for weeks and had half a kidney removed.
The brazen Brunswick attack in front of families and school children near the Barkly Square Shopping Centre sparked fears of a new gang war.
Police will investigate whether a contract has remained on Mitchell's life or if the latest incident was part of new tensions.
Mitchell is on bail after a raid in November on his former
Docklands address, where a stun gun and a large amount of cash were
Police last night confirmed a 38-year-old man was in the Royal Melbourne Hospital with what were "believed to be gunshot wounds".
It is not known how many assailants were involved in the shooting on Friday. The violence against Mitchell is likely to heighten tensions within the outlaw bikie underground. He was not well liked for his aggression towards rivals.
Police say they are trying to get witnesses to come forward, but Mitchell has not co-operated with past police inquiries and it is notoriously difficult to get anyone to talk about bikie gang-related incidents.
Jail gang Prisoners Of War, which was involved in the murder of Carl Williams, was linked to the Brunswick shooting, which is unsolved.
CCTV footage went missing from Doherty's gym, next to the Bandidos clubhouse in Weston St.
Mitchell resumed as sergeant-at-arms following his recovery and has travelled regularly to South-East Asia. He also has been seen around Melbourne wearing his bikie colours.
He had been linked with Tony Mokbel's former lover, Danielle McGuire.
Mitchell was seen talking to rival gang president Jay Malkoun at a Danny Green fight in November - his first public appearance since his shooting.
Mick Gatto and other underworld figures enjoyed the boxing with Mitchell from ringside seats.