According to South Yorkshire Police ... the man was arrested on suspicion of manslaughter on Tuesday -- 17 days after Johnson tragically died from injuries he suffered when Matt Petgrave's skate slashed him in the neck during an Elite Ice Hockey League game.

In announcing the arrest, cops did not say if Petgrave was the man they had in custody.

"Our investigation launched immediately following this tragedy and we have been carrying out extensive enquiries ever since to piece together the events which led to the loss of Adam in these unprecedented circumstances," SYP detective chief superintendent Becs Horsfall said of the arrest in a statement.

"We have been speaking to highly specialised experts in their field to assist in our enquiries and continue to work closely with the health and safety department at Sheffield City Council, which is supporting our ongoing investigation."

Johnson was playing for the Nottingham Panthers against the Sheffield Steelers in England when the tragedy happened.

Video from the arena showed as Johnson was crossing the blueline, Petgrave kicked his skate into the air ... and clipped the former Pittsburgh Penguins center in the throat. Blood immediately poured onto the ice -- and while Johnson was rushed to the hospital for emergency treatment, he sadly succumbed to his injuries.

Cops revealed Tuesday "a post-mortem examination confirmed he died as a result of a fatal neck injury."

"Adam's death has sent shockwaves through many communities, from our local residents here in Sheffield to ice hockey fans across the world," Horsfall said. "We know these communities will expect us to handle this investigation with the same professionalism, fairness and sensitivity as any other and request that members of the public refrain from comment and speculation which could hinder this process. Our thoughts remain with all affected by this devastating incident as enquiries continue."

The Panthers, meanwhile, had initially called Johnson's death "a freak accident."