A manhunt is underway to find a person who stabbed a newlywed computer-store manager in Melbourne's CBD on Wednesday morning.

Thirty-five-year-old Ronald Maskell, was stabbed in the shoulder and may have a punctured lung after the attack on Collins Street.

The Brighton man was opening a Hewlett-Packard service centre on Collins Street near the corner of Swanston Street when another man entered the second-floor office about 8.40am.

Mr Maskell approached the man, who was acting suspiciously and rummaging through a bag, and asked him, "Are you alright, mate?".