A father in his twenties has been arrested on suspicion of murdering his baby son, Gloucestershire Police confirmed on Friday.
Emergency services were called to a property in the market town of Cirencester, in east Gloucestershire, on Tuesday.
They were contacted over concerns for the health of the baby boy shortly before 1.20pm.
The infant was taken to Bristol Royal Hospital for Children, around 40 miles (1km) away.
He died later on Wednesday.
On Friday morning, police officers arrested the father from Cirencester on suspicion of murder.
A spokesman for Gloucestershire Police said: “Police are now investigating whether his injuries were non-accidental.”
The arrested man remains in police custody, the force spokesman added.
Officers did not reveal the age of the child on Friday.