McIlroy is suing Conor Ridge’s Horizon Sports Management over the cut his firm was taking from his earnings both on and off the course.
The bitter row over ??4.2m in fees has taken the pair all the way to the big business division of the Irish High Court in Dublin.
The case centres on McIlroy’s contract with Dublin-based Horizon and two other linked companies, the Malta-based Gurteen and Canovan Management, also based in the Irish capital.
In court papers when the case was launched in late 2013, it was claimed McIlroy signed up with Ridge’s agency at an informal meeting on the day of Horizon’s Christmas party in 2011 when the Northern Irishman was 22.
The world No 1 claims that fees charged by Horizon were almost four times what top 10 golfers pay to agents.
Horizon is counter-suing the four-time major winner for at least ??1.65m after breaking his contract early.
Provided an 11th-hour settlement is not reached, the case will be heard before the president of the High Court, Judge Nicholas Kearns.
The court case is expected to last between four to six weeks.