The former managing director of Leeds United FC is facing criminal charges in the United Arab Emirates over a tweet about the former owner of the club.
David Haigh has been in custody since May 2014 and was due to be released on November 16 last year after a Dubai court convicted him of fraud.
But on November 14 he was charged with slander of his former employees in relation to a comments on his Twitter account made eight months earlier when he was in prison.
A trial has been set for March 16 but non-governmental organisation Human Rights Watch has called for him to be released after his lawyer Alun Jones said he was concerned for Mr Haigh's mental and physical well-being.
The organisation's deputy Middle East director Joe Stork said: "If UAE businessmen can have their partners locked up when they don't like the tone of their tweets, one has to question whether the UAE is a safe place to make any form of criticism.
"The UK government should make very public calls for David Haigh's immediate release and scrapping of the criminal slander law."
Mr Jones said the problems emerged when Mr Haigh told his Dubai-based employer, Leeds United's former owner GFH Capital, that he intended to bring legal proceedings against it for outstanding commissions.
He was arrested in May that year when he flew to Dubai for a meeting.
Mr Jones, who did not represent Mr Haigh at his first trial, said his client had not been able to understand the evidence against him as it was in Arabic.
Human Rights Watch said it had been told that the Twitter account was being handled by a third party because Mr Haigh was in prison without access.