A tumultuous 24 hours for the UFC took another turn on Friday when lightweight title contender Max Holloway could not make the weight for the fight at UFC223, with American Al Iaquinta stepping in to face Russian Khabib Nurmagomedov for the belt.

As the sport's best-known athlete, Conor McGregor, faced assault and criminal mischief charges after a violent incident at the Barclays Center in Brooklyn on Thursday, the UFC had hoped to get back to normal at the weigh-in.

The 29-year-old McGregor, who won the lightweight belt in November 2016 but never defended it, was set to be replaced as undisputed champion by the winner of Saturday's title fight between UFC featherweight champion Holloway and Nurmagomedov.

But Hawaiian Holloway, who took the fight on six days' notice after an injury to American Tony Ferguson, was ruled 'medically unfit' to fight by the New York State Athletic Commission as he struggled to make the 155-pound limit.

After a frenzied afternoon of negotiations, the UFC announced that 30-year-old Iaquinta would step up to face Nurmagomedov in his home town of New York in the UFC223 main event on Saturday.

As Iaquinta, who is on a five-fight win streak, came in just over the 155-pound limit, only Nurmagomedov can be crowned champion should he emerge victorious from the bout, the UFC said