Errol Spence Jr. is OUT of his fight against Manny Pacquiao -- the welterweight champ was forced to withdraw from the huge event due to a nasty eye injury.
Of course, the 31-year-old was set to face off with the 42-year-old star on August 21 at T-Mobile Arena in Vegas ... a fight that's been hyped up for months.
But fans will have to wait to see Spence and Pacquiao duke it out in the ring ... with WBA welterweight champ Yordenis Ugas -- who was already on the card as a co-feature -- stepping in as a replacement.