Pacquaio lost out via a highly-disputed decision in Brisbane and Arum said he knew as early as December of last year that Australian Horn would be a big threat should the fight eventually be made.
“He is a tough, tough kid and he is probably the strongest welterweight in the world,’’ Arum said.
“If it was just an alley fight, I would pick Horn against any welterweight out there. Obviously these are not alley fights, but Manny Pacquiao has never fought a fighter as strong, physically, as Horn.
“Horn was relatively unknown because nobody would listen to me, but I saw him fight last year in Auckland on the Parker-Ruiz card, and I told everybody that he was a big, strong welterweight who would give Manny Pacquiao or any other welterweight trouble,’’ he added.
Pacquiao is currently contemplating his next move, with a rematch against Horn already contracted at the Filipino’s desire.
Other options include British fighters Kell Brook and Amir Khan or a potential move back down to challenge the winner of Terence Crawford v Julius Indongo – trouble-free sanctioning permitted.
In the new WBO rankings, Pacquiao retained the mandatory position at 147, which would possibly be used to set-up the Crawford fight at 140lbs if an agreement can be made with current number one Antonio Orozco.
Crawford and Indondo meet next month with at least three versions of the super-lightweight championship set to be on the line.
