Police were called at around 11:35am on Thursday, 30 May, to reports of a man assaulted in Plaistow Park, E13.
Officers and London Ambulance Service attended and the man, aged 61, was taken to an east London hospital with a serious head injury. He remains in a critical condition.
His next of kin are aware.
Two men were subsequently arrested as part of this investigation.
A man aged 29 was arrested near to the scene on suspicion of GBH – he has since been released under investigation.
Mohammed Metowlli, 23 of Bemersyde Point, Dongola Road E13, was arrested at an address in Plaistow later on that same day. He has subsequently been charged with GBH and kept in custody to appear at Thames Magistrates’ Court on Saturday, 1 June.
Enquiries into the circumstances continue by officers from the North East Command Unit.