A 35-year-old man was in a critical condition in hospital after a fight in Ipswich town centre on Saturday night.
A Suffolk Police spokesman said the incident took place in the Cromwell Square car park at 2100 BST.
The victim was taken to Ipswich Hospital, but was later transferred to Addenbrooke's Hospital in Cambridge for treatment.
The spokesman said a 44-year-old man was being held for questioning and witnesses were being sought.
Police have not released the names of either man.