Tobias Richter, the head of National Express in Germany, said the Bavarian state procurement chamber had expressed concern about the company's financial strength.

"I assume that we will take this to the state court in Munich," Richter said.

He added that as long as the case was being heard at the state court it would prevent any other rivals from winning the contract to operate the Nuremberg rails.

The company said earlier this year it had been named preferred bidder by the Bavarian transport authority to run Nuremberg S-Bahn services from December 2018, taking over from Deutsche Bahn's DB Regio unit.

It has already also won a contract to run train services in a western region of Germany

(Reporting by Markus Wacket; writing by Erik Kirschbaum; editing by Susan Thomas)