Emiliano Sala, a striker who had just signed with Cardiff City, was killed in a plane crash in January.
The pilot, David Ibbotson, was also killed in the crash.
Sala, 28, had been travelling from Nantes to Cardiff when the plane crashed into the sea near Guernsey.
His body was recovered from the ocean floor in February, but Mr Ibbotson’s has never been found.
READ MORE: Emiliano Sala’s father Horacio dies at 58 three months after Cardiff star’s tragic death
A spokesperson for Dorset Police said a 64-year-old man from North Yorkshire had been arrested and released while investigations continue.
They added the families of the two men who died had been informed about the arrest.
Det Insp Simon Huxter, of the force’s Major Crime Investigation Team, said: “As part of this investigation we have to consider whether there is any evidence of any suspected criminality and as a result of our inquiries we have today, Wednesday 19 June 2019, arrested a 64-year-old man from the North Yorkshire area on suspicion of manslaughter by an unlawful act.
“He is assisting with our inquiries and has been released from custody under investigation.”
Det Insp Huxter urged people not to speculate about the identity of the man as it could hinder the investigation.
What happened to Emiliano Sala?
The single-engine Piper Malibu aircraft carrying Sala and Mr Ibbotson left Nantes, north-west France, at 7.15pm on Monday, January 21.
It had been flying at 5,000ft (1,500m) over the Channel Islands when Mr Ibbotson contacted air traffic control and requested to descend.
The plane lost contact while at 2,300ft (700m) and disappeared off radar near the Casquets lighthouse, infamous among mariners as the site of many shipwrecks, eight miles north-west of Alderney.
Sala sent a WhatsApp voice message before the flight, which was released to the press, in which he sounded conversational and jokey.
He recorded himself saying he was “so scared” in a humorous tone and that he was “on a plane that seems like it is breaking apart”.
Rescue crews searched about 1,700 square miles of land and sea in the Channel Islands, before calling off the search on January 21.
They said the chances of finding the passengers alive became “extremely remote”.
Shipwreck hunter David Mearns found the plane wreckage on 3 February, 220ft (67m) below water, using sonar after a crowdfunding appeal to find the aircraft raised £340,000 (371,000 euros).
Divers managed to confirm that a body – which turned out to be Sala – was still in the fuselage, and managed to retrieve it.
Mr Sala’s body was brought to Portland and Dorset Police has been carrying out inquiries on behalf of the coroner since.
Earlier this month, two people were summonsed to court after sharing a photo apparently showing Sala’s body after a postmortem, and criminal proceedings are not underway.