The five-weight world champion said he favours the American because of his unbeaten record while the Filipino has lost two of his past five bouts.
Speaking in Sheffield, the American told Sky Sports News: ???Psychologically he [Pacquiao] won???t think that going into the ring that he has lost two fights.
???Mayweather has not lost at all.
???It will give him a little edge but not too much.???
He added: ???You don???t know, one punch could end it all.
???One punch could turn the tables around.???
Leonard also compared the showdown between Mayweather and Pacquiao to his victory over Marvin Hagler in 1987.
He added: ???I came out of retirement a couple of times and then I came back for Marvin Hagler.
???It was a fight that people thought would be one-sided because I???d been out of the ring so long.
???I???d had one fight in five years, Hagler hadn???t lost in 11 years.
???He was a bigger man and had other attributes.
???But it lived up to expectations because no one thought I could go the distance.???