Completed in 1927, the circuit was built to showcase German auto engineering and racing prowess. After Niki Lauda's Ferrari exploded in a fireball on the Nuerburgring in 1976, the race track has been deemed too dangerous for Formula One.

The European Commission, which acts as the competition watchdog for the 27-country EU, in its 2014 decision said that motor sport industry supplier and new track owner Capricorn Group did not receive state aid as the sale was transparent.

Ja zum Nuerburgring eV and U.S. company NeXovation, which lost out in the tender process, then challenged the EU ruling at the General Court, Europe's second highest, but lost. They subsequently appealed to the EU Court of Justice (CJEU).

The CJEU backed the two parties.

"The Commission must re-examine whether the sale of the Nürburgring in 2014 entailed a grant of state aid," judges said.

"In the same year, it wrongly ruled out the presence of doubts as to the possible existence of an advantage conferred on the buyer and decided not to open a formal investigation procedure."

The cases are C-647/19 P and 665/19 P Ja zum Nürburgring and NeXovation v Commission.

(Reporting by Foo Yun Chee; Editing by Mark Potter)

By Foo Yun Chee