A 15-year-old boy has been arrested on suspicion of grave and criminal assault and released on bail whilst enquiries continue into the incident, which took place Bath Street at around 20:20 on Monday 10 April.
The 15-year-old was accompanied by several other boys and one girl — all are believed to be aged between 15 and 16.
The alleged victim was taken to hospital due to facial injuries he sustained and was still being treated at the time of writing.
It is believed that the youths and the man were not known to each other.
Anyone who may have information is asked to contact police on 612612 or the independent charity Crimestoppers anonymously on 0800 555 111 or via their Anonymous Online Form at Crimestoppers-uk.org.