The two-time major winner is due to begin a High Court action in Dublin today in a bid to terminate the contract with his former agent.
Lawyers for McIlroy, 24, are expected to ask that his action against Horizon Sports Management is fast-tracked to the Commercial Court.
McIlroy signed up to Horizon, a Dublin-based firm run by Conor Ridge, in 2011. But he announced he was splitting from the firm last month and setting up his own management team.
His legal affairs are being handled by A&L Goodbody who are expected to describe Horizon’s sign-up deal to the court as exploitative.
Horizon charges 20% on McIlroy’s massive Nike advertising deal, which is worth an estimated €74m over five years. It charges 15% on his other endorsements, including lucrative deals with Omega, Bose and Santander.
McIlroy will claim that Horizon was aware of his lack of business experience when they signed him up, and that very confined terms for early termination of the contract were unfavourable to his interests.
He is also expected to claim that Horizon’s fees are more in line with those levied on unproven golfers.
Agents can charge fees of up to 10% of a player’s on-course earnings as well as a higher percentage of any endorsement deals it generates.
Horizon, which has declined to comment, is mounting a vigorous defence, and will claim that McIlroy is in breach of a contract he entered into willingly.
Horizon is expected to seek compensation through the courts if an agreement cannot be reached between the sides.
Experts estimate that it could cost McIlroy at least $6m (almost €4.5m) to walk away from the Horizon contract.
McIlroy announced his decision to break with Horizon last month just 23 months into a contract which had at least another three years to run.
His decision came soon after Horizon generated several lucrative endorsement contracts for the Ulsterman — considered by some to be some of the most lucrative endorsements in sports history.
McIlory also set up his own company — Rory McIlroy Incorporated (RMI) — to manage his affairs. His new management team is headed up by Donal Casey, who worked with Horizon as director of strategy until last December.
The Rory Foundation for charity is run by Barry Funston, a longtime friend of the McIlroy family.
Both Casey and Funston will serve on the RMI board, together with Rory’s father, Gerry McIlroy.
McIlroy’s media relations are being handled by The Communications Clinic, led by Terry Prone.
McIlroy left International Sports Management just four months after winning his first major at the US Open at Congressional, to join Horizon, which also represents Graeme McDowell.