The horse racing magnate, John Magnier, and Coolmore stud farm in County Tipperary are to vigorously contest a legal action launched by the Manchester United manager, Sir Alex Ferguson.
Sir Alex has begun High Court proceedings to try to obtain a ruling that he owns a half share in the stallion, Rock of Gibraltar, and is entitled to half the profits earned at stud.
It is estimated that the former champion racehorse could generate a turnover of up to €9m a year in stud fees.
Sir Alex claims he was given a 50% share of the racehorse by Mr Magnier as a present.
In a statement, Mr Magnier and the Coolmore stud farm say they consider Ferguson's claims to be without merit, and they will vigorously contest them.
Last month, John Magnier and his business partner JP McManus increased their shareholding in Manchester United to just over 23%.
