Police have released vision of a man who may be able to help with the investigation into a "one punch attack" in South Brisbane on Saturday morning.
About 10.15am a man was walking along Melbourne Street when he became involved in an argument with another man who was jogging in the opposite direction.
The pair exchanged words in passing and the jogger has turned and punched the victim in the face.
Police believe the victim lost consciousness and fell to the footpath, while the attacker allegedly walked off towards Merivale Street.
The man police want to speak to is described as about 170cm with short dark hair and was wearing black shorts with a red shirt tucked into them and white running shoes.
The 48-year-old injured man remains in the Princess Alexandra Hospital in a critical condition.
A group of bypassers witnessed the assault and are assisting police with their enquiries.
It is believed the two men did not know each other.
Police are urging anyone who recognises the man or has further information to contact Crime Stoppers on 1800 333 000.
This latest one punch attack comes after a Gold Coast man died from a punch allegedly thrown by his own son in the Brisbane CBD in July.
In January, police said the public were not heeding advice about one punch attacks after a man died on the Sunshine Coast and teenager Cole Miller was killed in Fortitude Valley.