The man, believed to be in his late 40s to early 50s, hasn't been formally identified, but the nearby Jalalia Jaamé Mosque in Rochedale said in a Facebook post that the imam Jalal Uddin had died.
Greater Manchester Police stepped up patrols to reassure the community. They acknowledged that there was much speculation about the death on social media, but urged people to allow them to investigate.
"The cause of his death is yet to be confirmed, we recommend that you do not speculate but rather wait for the facts to be established by the police," the mosque said.
Uddin went to evening prayers Thursday night, then went to a friend's house for dinner, localssaid. He left the friend's house around 8:40 p.m. and took a shortcut through the playground. Passersby found him with the head injury just before 9 p.m. and tried to revive him, but he passed away in hospital.
A post mortem was due to take place Friday afternoon.
“Our investigation is at an early stage but we are keen to hear from anyone who may have been in the area near to where he was found in Wardleworth last night, as we work to establish how this man came to suffer his head injury," Detective Superintendent Jon Chadwick said in the police statement.
Rochdale MP Simon Danczuk paid tribute to Uddin, saying he was a pillar of the community.
“He was a well regarded, peaceful man, a very, very gentle man. He was well thought of in his local Mosque and among the Bangladeshi community," he said.
Mohammed Shafiq, chief executive of the Ramadhan Foundation, a Muslim community organisation, said: “The news that a popular local Imam from Rochdale was murdered last night returning from prayers at a local mosque is shocking and tragic. Whilst it is too early to speculate about the circumstances of the murder we would urge the community of Rochdale to stay united and calm."
"We would urge all local mosques in Rochdale to consider emergency security precautions and facilities to help local people return home safely from the mosque."