Manitoba's police watchdog has concluded the death of a man found naked and yelling behind the legislative building in Winnipeg was not the result of any action or inaction by police.

The Independent Investigation Unit of Manitoba (IIU) says the man lost consciousness as police were trying to restrain him in September 2019 and he died in hospital a week later.

The IIU says witnesses reported seeing the man fall and possibly hit his head before police arrived and none reported seeing any indication that he was assaulted by officers.

It adds that it has concluded its investigation after the cause of death was determined to be an anoxic brain injury due to cardiac arrest complications and probably excited delirium.