Police allege the man was walking along Albert St, Goodna, about 1.30pm Monday when he passed a 19-year-old man walking in the opposite direction.

The teenager then turned and punched the 56-year-old in the back of the head, causing him to fall to the ground and hit his head, police allege.

The alleged victim was taken to the Princess Alexandra Hospital with a life-threatening head injury.

A 19-year-old Redbank Plains man has been charged with grievous bodily harm and is scheduled to appear in Ipswich Magistrates Court today.

Anyone with information should contact Crime Stoppers on 1800 333 000 or at crimestoppers.com.au.