Rory McIlroy, fresh from a weekend victory in Dubai, is suing Conor Ridge's Horizon Sports Management over the cut his firm was taking from his on and off course earnings.
On Tuesday the world number one is in Dublin to contest the case in court.
The bitter row over £4.2million in fees has taken the pair all the way to the big business division of the Irish High Court.
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.
The golf star, who took up the game as a youngster in Holywood, Co Down, and now has a home in Florida, claims the terms were inferior to those given to other top 10 players including fellow countryman and major winning friend Graeme McDowell, who was in the same stable.
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.
The golfer, whose address at the time was given as Avenue Princess Grace in Monaco, alleged he was exploited, misled and taken advantage of when he joined the Dublin agency.
The court heard he had no legal advice or knowledge of negotiating before he signed up, and trusted them to charge the appropriate rates.
McIlroy's case will be heard before the president of the High Court, Judge Nicholas Kearns, unless the two sides attempt an 11th hour settlement.
The dispute involves McIlroy's claim that Horizon charged almost four times what top 10 golfers pay to agents.
The pre-tax rates were set at 5% of prize winnings and 20% of sponsorship and appearances money, a charge his lawyers claim is reserved for an "inexperienced or unproven golfer'', the court heard last year.
McIlroy's business interests are now overseen by Rory McIlroy Incorporated, which is headed by Donal Casey, formerly of Horizon, his father Gerry and family friend and business executive Barry Funston, who also oversees much of the golfer's charitable work under the Rory McIlroy Foundation.
Another dispute in the case is an alleged 166,000 euro (£141,000) donation to Unicef on the eve of a trip to Haiti when McIlroy was an ambassador for the charity.
There was another row over Horizon using complimentary airline seats on a flight to Abu Dhabi booked by tournament organisers in McIlroy's name.
The young golfer's career soared in the year after he signed for Ridge from Chubby Chandler's stable, earning more than £10m in 2012 before hitting a slump to earn about £2m in prizes.
He was with the company when he won the 2012 PGA Championship, rose to number one in the world and signed a five-year sponsorship deal with Nike, said to be worth in excess of £60m.
A dip in form followed and his engagement to tennis star Caroline Wozniacki ended, but the Northern Irishman has four majors to his name.
And if recent form on the course offers any insight into his demeanour in the face of a potentially ugly court case, McIlroy appeared focused when picking up his latest trophy.
He is now favourite to complete the career grand slam of golf, aiming to have the commercial dispute over before vying for a famous green jacket at the US Masters in Augusta in April.
Unless both sides agree to last minute mediation - a plea for which already failed last December - the relations between arguably the world's most marketable sports star and a Dublin-based agent are set to play out in public over the next four to six weeks.
Ridge's Horizon is counter-suing McIlroy for at least £1.65m after breaking his contract early.
