The upcoming federal election in Germany is not going to throw Brexit negotiations off course, but the U.K. needs to face the reality that Brexit is not the greatest priority for the EU, according to the head of the European Stability Mechanism (ESM).

The EU will remain united in its approach to Brexit negotiations regardless of the outcome on September 24, Klaus Regling, managing director of the ESM, told CNBC Tuesday.

"I see a great unity among the EU member states and I don't think the German election is going to derail that," Regling noted.

However, he insisted that the vote, the last of three major elections across Europe this year, shows that that EU member states have other equally important issues on their agendas.

"They (the EU) have deliberately decided to be very transparent, so there should be no surprises," Regling continued, referring to the aftermath of Germany's vote. "But, in general, in this country (the U.K.) people must realize there are also some other priorities on the continent.

"Brexit seems to be the only topic in this city, and maybe in the country. In the continent it's quite different: it's one topic among many."