Sir Alex Ferguson, Britain's most successful soccer manager, has started court action against John Magnier, owner of Ireland's Coolmore Stud, as the dispute between them over top racehorse Rock Of Gibraltar, who is now a globe-trotting stallion, reaches a climax.Sir Alex, who it is believed is claiming 50% of Rock Of Gibraltar's stud earnings, issued a writ in Dublin, Ireland's capital.This brought an immediate response from the other side, with the release of a statement which said: "Coolmore Stud has been advised that legal proceedings have been issued against Mr. John Magnier by Sir Alex Ferguson alleging certain ownership rights for the stallion Rock of Gibraltar. Coolmore Stud and John Magnier consider the action to be without merit and it will be vigorously defended. As this is a legal matter, no further comment will be made."The disputes centers around what sort of agreement Ferguson had with Magnier, a worldwide force in the bloodstock world, when the latter gave the manager of Manchester United a half-share in Rock Of Gibraltar towards the start of the horse's racing career. Magnier's wife Sue owned the other half.Rock Of Gibraltar then won a record seven successive group I races carrying Ferguson's colors and the Danehill colt started stallion duties this year, standing in Ireland and then shuttling to Australia.Neither side will comment officially but it is understood that Ferguson thinks he was offered 50% of the prize money won by the horse or 50% of the stallion income, choosing the latter, while Magnier believes he offered 5% of the prize money or a nomination to Rock Of Gibraltar each year.Therefore, the gulf between the two sides is considerable. Attempts to reach an agreed settlement have apparently been made, with £7-8 million reportedly rejected while a newspaper report on Nov. 23 claimed that the case would never come to court because a settlement of up to £20 million could be on the table.The dispute has generated enormous media coverage, partly because Magnier, along with J. P. McManus, owns just over 23% of Manchester United and Ferguson is currently considering a new four-year contract.Rock Of Gibraltar's stud earning are estimated to be worth at least £12 million a year and could be as high as £15 million.