Dr Gray's father David died after Dr Ubani gave him an overdose of diamorphine on his first UK out-of-hours shift. Dr Gray and his brother Rory have sought to raise the profile of the case by speaking out both in the UK and Germany.
But lawyers acting for Dr Ubani have launched a legal bid in Germany to stop Dr Gray and his brother Rory from talking to the press.
Dr Gray said this month: 'We had a letter from Dr Ubani's lawyer asking us to sign a paper saying we would not go to the press, to pay his lawyer costs and pay a EUR25,000 fee if we breach the injunction.'
Efforts to agree reconciliation between the brothers and Dr Ubani at a 9 August hearing in Bavaria failed. A further hearing takes place on 25 August.
Dr Ubani faces a fitness-to-practise hearing on 18 August where the German equivalent of the GMC plans to make him sit a written exam to test his medical skills which could see him suspended from clinical practice.