A court sitting in the case of Silvio Zammit, during which the head of the EU anti-fraud agency (OLAF) was expected to give evidence was postponed today.
Dr Kessler had been due to give evidence by video conference.
Also due to give evidence today was another member of the agency who investigated the case, Luis Romero.
Mr Zammit stands accused of trading in influence as the European Commission was drafting a new Tobacco Directive under John Dalli's guidance.
Mr Dalli was forced to resign from the Commission in October 2012 after Olaf concluded there was circumstantial evidence to show that the former commissioner was aware of Mr Zammit’s alleged bribery dealings.
This was to have been the first time that Dr Kessler gave evidence on the case in Malta.
Unofficial sources said arrangements had not been made on time for Mr Kessler to give evidence today.