An MP has called on the government to stop Bulgaria joining the European Union until a retrial is ordered for jailed football fan Michael Shields.
Michael Shields has always denied carrying out the attack
Michael Shields, 19, of Wavertree in Liverpool, was convicted in July of the attempted murder of barman Martin Georgiev who was hurt in a bar brawl.
Another man, Graham Sankey, of Anfield, has signed a confession but this was not accepted by the Bulgarian court.
Liverpool Riverside MP Louise Ellman brought up his case in the Commons.
"I recognise that ministers cannot interfere in the Bulgarian judicial process but I ask them to exert their influence on the Bulgarian authorities and urge them to conduct an inquiry or order a retrial," she said.
"It is a matter of justice."
Shields has denied carrying out the attack in the Black Sea resort of Varna in May.
He had travelled there on holiday after watching Liverpool beat AC Milan at the Champions League Final in Istanbul and claims he was asleep in bed at the time when Mr Georgiev was attacked.
But the court rejected his claim, and found him guilty of hitting the barman on the head with a rock.
An appeal to reduce his sentence failed earlier this month, but the court reduced his £70,000 fine to £42,000.
A further appeal is pending at the Supreme Court in Sofia.
Mrs Ellman said with EU entry being discussed this month, it is "a very critical time for Bulgaria".
She said the EU already had concerns over the country's human rights issues and this case could be crucial.
Europe Minister Douglas Alexander said: "We will continue to do all that we can to assist the Shields family.
"We are unable to interfere with judicial process in other countries but we remain committed to do all that we can properly do to ensure Mr Shields' welfare. We take Mr Shields' case very seriously."