Bob Arum -- Manny Pacquiao Rematch With Juan Marquez Will Happen

Manny Pacquiao ain't retiring ... and he WILL fight Juan Manuel Marquez for a 5th time -- at least according to boxing promoter supreme Bob Arum.

Arum was outside Madeo last night when he dropped the bombshell boxing fans have been waiting to hear ever since Marquez KO'd Manny's face into the canvas on December 8.

Arum said Manny is vacationing in Israel, but when he gets back ... "We're gonna, I think, do another fight with Juan Manuel Marquez. That was a great fight."

And even though a lot of critics think Manny should hang up the gloves -- Bob thinks he'll have a decent shot in a rematch, saying ... "He ran into a really good right hand, and we'll see what happens next time."