Carwyn Edwards, 39, has been in hospital in Tucson, Arizona, since the start of the year after an illness led to the partial amputation of both legs.
His family fear they could face substantial medical costs.
Medical insurer Cigna said it was addressing Mr Edwards' concerns.
A campaign to raise funds for Mr Edwards, who has lived in the US for 13 years, has raised Â£38,000, however the latest news that the benefit payments will stop in a fortnight has created more uncertainty about his future treatment.
Mr Edwards' brother, Aled Edwards, will be flying to Arizona shortly to try to resolve the issue.
He also hopes to find out what arrangements can be made to transport his brother to the UK continue his recovery.
Cigna said it could not discuss the case at length because of confidentiality laws.
A spokesman said: "We can say that our case workers have been in communication with this individual and will continue to address his concerns directly with him."
The family of an Anglesey man who is seriously ill in the United States have said they are concerned about his future treatment after insurers said his medical benefits would be stopped.