The Frenchman, Chadd Attardi, 20, has had his passport confiscated and may still face charges even after compensation has been agreed.
The German, Erick Heim, 55, is no longer on Phuket so lawyers on both sides are involved in negotiations.
Days are continuing to pass since the incident in the water off Paradise beach, south of Patong, on February 28.
Colonel Anukul Nuket is the Deputy Superintendent at Kathu Police Station, which is located in Patong.
''Mr Heim needed treatment for head and neck injuries in the intensive care unit at Bangkok Hospital Phuket and the bill mounted to 400,000 baht,'' he said.
''He is also seeking a further 300,000 baht because he knows he will need more surgery back in Germany at a later date.''
Insurance covered 150,000 baht of the hospital costs and the jet-ski rider has offered an extra 100,000 baht towards costs on Phuket.
''The complicating factor is that with lawyers now involved, it's not just about the cost of treatment on Phuket and in Germany but about the legal costs as well,'' the colonel said.
''I understand the parents of the Frenchman have sent a considerable sum but it is less than what the
German is asking and does not include an allowance for legal fees.''
Mr Attardi has been charged with riding a jet-ski without a licence and with reckless riding endangering others. He is out on bail from Phuket Provincial Court.
Another German was struck by a jet-ski while swimming off Naka island on March 10 but the injury was not serious and police did not become involved.