It is on the conflicting accounts of Gribkowsky and 83-year-old Ecclestone that the whole corruption scandal turns.
Gribkowsky, already serving an eight and a half year jail sentence for receiving Ecclestone's money, is expected to confirm prosecutors' claims that he was paid in order to influence the sale of F1's commercial rights and keep Ecclestone in power.
"The accusations are based on statements by Dr Gribkowsky that are incorrect, misleading and incoherent," Ecclestone said in an opening written statement to the court two weeks ago.
Briton Ecclestone, however, insists he only paid Gribkowsky because he was being blackmailed over his personal tax affairs in Britain.
"Many people have asked, 'How can you put someone like Bernie under pressure?'" Ecclestone's statement added. "You can, if you find the right lever. Dr Gribkowsky succeeded in finding it.
"It was clear to me he wanted money in any case under whatever headline," Ecclestone continued. "From today's perspective, this (paying him) may not have been a rational decision. But at the time, I thought 'This man is dangerous'."
Gribkowsky is one of almost 40 witnesses who will also testify in the 26-day trial, the news agency added.