Dieter Kempf, president of the Federation of German Industries, claimed the Brexit Secretary could not be taking negotiations seriously if he was planning on taking Bank Holiday Monday on holiday.
Mr Kempf also told Bloomberg that he was “skeptical” about progress being made between the EU and UK in the third round of negotiations.
He said: “I just can hope that we see that progress, I have to admit that I am skeptical.
“I just remember that the British delegations thought about taking this date or not taking it because of a national holiday at home.
“That clearly means that in their opinion they thought that a national holiday was more important than continuing the negotiations.
“We have just a two-year time frame to finish it and more than half a year has already gone.
“I can just hope that there is some achievement.”
Mr Davis did not take Bank Holiday Monday on holiday and instead traveled to the continent to continue Brexit talks.
The German industry chief highlighted how important it was for the EU and UK to reach an agreement before the Brexit deadline in March 2019.
Mr Kempf reiterated how unprepared both the European Union and the United Kingdom were when starting Brexit talks.
“I think that we are just not well prepared from my point of view,” he added.
“We all, not just the Brits and not just the remaining 27, are very dependent on the result of these negotiations.
“I want both parties, the European Union as well as the UK to take those negotiations seriously because they are of a severe economic importance.”
Before the third round of negotiations, Michel Barnier claimed the UK’s position was unclear, despite the UK outlining its Brexit position with papers last week.
“We need UK papers that are clear in order to have constructive negotiations. And the sooner we remove the ambiguity, the sooner we will be in a position to discuss the future relationship and a transitional period,” he said.
The comments came after the UK Government released a number of Brexit papers which clarified Britain’s position over issues such as the Irish border, customs union and European Court of Justice.
President of the European Commission also took a swipe at the UK insisting papers presented by the UK last week were not “satisfactory”.