A decision is expected this afternoon on an appeal to the Court of Arbitration of Sport (CAS) by the Irish showjumper Denis Lynch.
Lynch filed an application at the CAS to challenge a decision of Horse Sport Ireland not to select him for the 2012 Olympic Games.
A panel began hearing the case in London at 8pm last night.
CAS has not commented any further on the procedure.
Lynch was dropped from Team Ireland after his horse Lantinus tested positive for hypersensitivity at the Nations Cup event in Aachen, Germany three weeks ago.
Cian O'Connor was selected as his replacement, to join Billy Twomey in the event at Greenwich Park.