The gun used in a Melbourne car park shooting that left a man injured may have been an air rifle, a witness says.

A Campbellfield man, 21, took himself to hospital with at least one gunshot wound on Monday night.

Police suspect he was targeted while outside an indoor sports centre in Coolaroo about 8pm on Monday.

The gun is yet to be identified but Roger Fredrick from a nearby business says there are only small dents in metal signs hit during the attack.

"We didn't even hear anything ... we would have heard something if it was a bigger gun," he said on Tuesday.

No one else was injured in the shooting.

Another organisation occupying the complex - the Hume Islamic Youth Centre - says the incident had "nothing whatsoever" to do with them.

"We recognise the need to work closely with the youth to keep them busy with what benefits them and benefits the community," HIYC management says in a statement posted on Facebook.

The Armed Crime Squad is investigating.