Mayweather faces the Filipino superstar with the WBA, WBC and WBO welterweight belts on the line in the MGM Grand on Saturday night.
However, Mayweather will be risking his undefeated record of 47-0 and the winner can claim to be the sport???s best pound-for-pound fighter of their generation.
???Manny was very relaxed, taking everything in his stride and that???s what you would like to see in a fighter, especially if I was Freddie Roach,??? Gallagher said on Sky Sports News HQ.
???I think Floyd will have more nerves than he has ever had before because the pressure is truly on him in this fight.???
Gallagher admits he is fan of Roach and his fellow trainer???s world famous Wild Card Gym.
???It???s an unbelievable set-up,??? added Gallagher. ???It???s a typical Hollywood set-up, you???ve got the stars there; Micky Rourke, Mark Wahlberg, and you???ve got Manny Pacquiao, from the Philipines, who???s like a god over there from that part of the world.
???Last time we were over there, you had a guy called Paul, who???s 80-odd, comes in, pays his five dollars and goes on the bag. That???s how it is, you have the boxing stars and then you have your normal people coming in, paying the five dollars and working the bag.
???That???s the atmosphere of it all and I know down there they are absolutely rooting for Manny to pull this one off.
???As for Freddie Roach, I???ve heard Freddie describe Manny as his son, he has no children but if he was to have one, Manny Pacquiao would be his second son.???
Pacquiao is reportedly 4lbs under the 140lbs welterweight limit ahead of Friday???s weigh-in which Gallagher says reveals the Filipino???s tactics.
???Manny has come through the weight divisions and I feel him being 4lbs under shows you the game plan for the fight,??? added Gallagher.
???He???s going to use a lot of speed and a lot of fast movement. Floyd Mayweather will most probably only go in the ring himself 5 or 6 lbs over the weight limit on the night, so I don???t see that having any bearing on the fight.???
When pushed for an answer on who would win Saturday???s fight, Gallagher plumped for the outsider in the two-horse race. ???Pacquiao, controversially,??? replied Gallagher.