Police were called to a disturbance on Devana Road in Highfields yesterday morning,.
A man was arrested close to the junction of Glossop Street and Osmaston Road at around 8.30am but he was then taken to Leicester Royal Infirmary for treatment.
He died around four hours later.
The exact cause of death is not known at this time and the man has not yet been formally identified.
Leicestershire Police has referred the matter to the Independent Police Complaints Commission (IPCC).