Filipino icon Pacquiao was expected to fight unbeaten American superstar Floyd Mayweather Jr on the same night but a row over random blood testing forced the cancellation of their 2010 super-fight, although Top Rank supremo Arum has suggested it could still happen later this year.
Pacquiao, widely regarded as the best pound-for-pound fighter in the world, will now face Bronx-based Clottey (35-3, 20 KOs) of Ghana.
The hard-hitting Clottey is coming off a split-decision defeat by Miguel Cotto last June, a fight that some felt he won, and Arum has insisted Pacquiao will give his opponent the respect he deserves (Pacquiao points win 4/5 Pacquiao v Clottey-WBO Welterweight Title).
"This is a competitive fight, as competitive as the Cotto fight (Pacquiao beat Cotto last November) going in," Arum said.
"We got a tremendous deal at the site. It's a big event and I think we'll do unbelievable."