PC Glen Oliver set up a gym in Crawley with Daniel Bell, from Horley, who was convicted of GBH with three Surrey men at a retrial in Crete in September.
Robert Hughes was left brain-damaged after he was attacked in Malia in 2008.
The Metropolitan Police has told the PC his business is not compatible with his role. PC Oliver, who is appealing, said he believed he could still run the gym.
Mr Hughes, 35, a former Oxford United player, was attacked outside a nightclub, stabbed with a broken bottle, stamped on, and left in a coma.
Mr Hughes' mother, Maggie, said: "How many more times do we have to explain the courts have made a decision and the Metropolitan Police should be now looking at it seriously that this business interest should not be going on?"
The BBC has seen an email from the Metropolitan Police which states the officer is not able to continue involvement with the gym while the appeal is ongoing.
But PC Oliver told the BBC he understood he could run the gym while the appeal was pending.
He said he met Bell a long time after the assault, he had every sympathy for Robert Hughes and had asked to meet his family face-to-face.
The four attackers were originally convicted in 2012.
In 2013, PC Oliver sought permission to set up the gym.
After Mrs Hughes complained, the Metropolitan Police found no evidence of misconduct but the IPCC upheld her appeal.
Det Con Leanne Henery, who was also involved in the opening of the gym, has ended her association with the facility.
Six weeks ago, the four attackers were convicted at a retrial and each given a three-year suspended jail term.
A police spokesman said: "The Metropolitan Police Service has informed the officer that this business interest is not compatible with the role of a serving Metropolitan Police officer.
"The officer is appealing this decision; the outcome of this appeal awaits."
A Met police officer is still running a Sussex gym with a convicted man after his employers told him to stop.