Former Nottingham Forest owner Fawaz Al-Hasawi is suing the club in the High Court for what he says is around £4.2m of unpaid loans.
It marks the latest in Forest's worsening relationship with their former chairman, who sold the club to Greek shipping magnate Evangelos Marinakis in May 2017.
Forest brought a legal case against Al-Hasawi 18 months ago, claiming unpaid money due from the sale.
Al Hasawi counter-sued, and his case will be heard in the High Court on Tuesday. It is thought a decision from the judges is likely next week.
Al-Hasawi purchased Forest in 2012 and oversaw nine different managers in a five-year period at the City Ground.
Forest avoided relegation to League One on goal difference in Al-Hasawi's final season at the club.
This season, they finished ninth, eight points off the play-off places.