Since the 1970s, a few horses have come close to winning the Triple Crown. In 2004, the largest crowd in New York Racing history, 120,139 people, attended the Belmont to see Smarty Jones attempt the 12th Triple Crown win. Smarty Jones finished second.
The scratch leaves a field of 11 in which Dullahan, the third-place finisher in the Kentucky Derby, will probably be favored.
Dale Romans, Dullahan's trainer, called the news "devastating."
"I thought it was going to be one of the biggest races in history, and we wanted him to be a part of it," Romans said.
The race will take place at approximately 6:30 p.m. ET at Belmont Park in Elmont, New York.
The time leading up to the Belmont Stakes has not been without controversy. A workers strike at Belmont Park was averted this week.
The racetrack's workers, who manage the grounds and put the horses in the gate, have been involved in a contract dispute with the New York Racing Association over wages and health care since 2010.
I'll Have Another's trainer will begin his 45-day suspension, handed down by the California horse-racing authorities, on July 1.
O'Neill was found responsible for high carbon dioxide levels in 2010 California Del Mar track racer Argenta's blood. However, he was not found guilty of "intentional acts" or any sign that betting was skewed toward Argenta in the race.
Despite that, O'Neill was still able to participate in the Stakes this weekend.