With Manny Pacquiao about to embark on what could be the last fight of his career, Floyd Mayweather Jr. has admitted that he didn’t have an easy time winning the May 2 mega-bout between the two welterweights. When he was recently asked to name the three toughest opponents of his career, Mayweather included the 36-year-old.

"I can say that none of them were easy," Mayweather said via BoxingScene.com. "Although I must say that Canelo was tough....Miguel Cotto [was tough]. Manny Pacquiao was very tough. Pacquiao is very good. He was better than I thought."

The fight ended in a unanimous decision for Mayweather, who solidified himself as the greatest boxer of his generation. But no fighter has truly come close to defeating the now-retired boxer, who ended his career in September at 49-0.

While Mayweather had never lost before 2015, his greatness was doubted by some because he still hadn’t faced Pacquiao. Even though the fight was considered to be “boring” by many casual fans who paid nearly $100 for the pay-per-view, Mayweather thinks it was the biggest win of his career.

"A lot of people said that I avoided this fight," Mayweather said via gmanetwork.com. "A lot of people said that I couldn’t win the fight. But I proved all of that was wrong, and therefore the fight against Manny Pacquiao is the most important for me."

Mayweather’s comments come days before Pacquiao is set to name the opponent for his next fight. Pacquiao will return to the ring on April 9 in Las Vegas, and he’ll let the world know who he’s set to face on Friday. It will be Pacquiao’s first fight since he underwent shoulder surgery after his loss to Mayweather, and Top Rank CEO Bob Arum says it will be Pacquiao’s last fight before he retires.

Pacquiao has reportedly been considering a fight with Timothy Bradley, Amir Khan or Terence Crawford, though Bradley is the overwhelming favorite to get the nod. Bradley recently won the WBO welterweight title that Pacquiao lost in May, and he has reportedly been in talks regarding the purse for a fight with the Filipino.

After Mayweather defeated Pacquiao, there were rumors that the two might have a rematch. Mayweather said he might give his opponent another shot, though he quickly changed his mind when he felt Pacquiao blamed his injury for the loss.

If Mayweather were to ever come out of retirement, it would probably be for another fight with Pacquiao. The May 2 PPV generated $600 million, and even if the rematch produced half as much revenue it would still be the second-most profitable bout in boxing history. Pacquiao’s decision regarding his next fight was delayed after it was expected to be made last week, and there’s no guarantee Bradley will be his next opponent.

But the chances of a rematch ever happening remain a longshot. Pacquiao could go out on top with a win against Bradley early next year, and the boxing world will have lost the sport’s top two stars in the span of just a few months.