FORMER Category III actress Stella Man So was never one of the big names to grace Hong Kong's prolific movie scene, but she was well enough known to attract the attention of an unknown assailant last month. Man was leaving a Central hair salon early one evening when she was attacked. The man punched and kicked her, then attempted to disfigure her by rubbing her face against the concrete pavement. A police officer was nearby and frightened the man off, but the fear of a repeat attack remains. Man says she does not know her assailant, but reported the incident to the police the following day. ''The attack was obviously planned,'' she said. ''The man waited for me on the steps, beat me up, but didn't rob me.'' Since starring in Erotic Ghost Story, one of the first sex-orientated movies to hit Hong Kong cinemas after the introduction of Category III films, Man has tried to move out of showbiz and the industry is rife with rumours she upset triad-backed film bosses by turning down sexy roles and refusing to remove her clothes for the cameras. Man keeps her private life as closely guarded a secret as her age, but she denies she has upset anybody in the film world. ''Although I've turned down just about all the Category III offers I've had, I am still on friendly terms with these producers,'' she said. ''I just can't think of anything I've done in the past four years that could have offended anyone.'' Nevertheless, sources within the industry suggested that she may have fallen foul of the same people who threatened former Miss Asia contestant Candy Chiu Ching-yee. Chiu filed a complaint with the police alleging an actress had told her over the phone that unless she fulfilled a ''contract'' to sing at a Christmas ball, she would end up like Ng Suet-man (the actress beaten up by slain Sun Yee On member Andely Chan Yiu-hing for refusing to strip for a movie role). Man is known to have been involved with a producer and the same actress involved in the Ng case. She admitted too that she had turned down offers of nude roles because she believed she would be ''protected'' by a producer friend. Whatever the outcome of this case, Man has announced she wants to shed her Category III actress tag and become a respected businesswoman, starting with a restaurant in China and then moving into importing - the kind of happy ending the Hong Kong movie industry has failed to provide her.