Andy Ruiz Jr admitted three months of partying and celebrating played a part in his defeat by Anthony Joshua on Saturday night.
The 30-year-old lost the world titles he won from AJ in June after a sluggish performance in which he never got close to the Brit.
He shrugged off any concerns about carrying too much weight in the build-up, but after his loss he apologised to his trainer Manny Robles.
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Ruiz Jr said: "My team were talking and I should've listened to them and not put on all this weight. I tried to do all this training on my own.
"I'm sorry, I should've listened to then more. I think I got too confident in myself but there's no excuses. He won one, I won one and I know for the third one I'm going to be a lot better.
"I think we started too late I don't want to say that three months of partying and celebrating I had affected me because to tell you the truth it kind of did."
Speaking to Sky Sports in the ring straight after the fight, Ruiz Jr said: "I didn't prepare how I should've and gained too much weight. He won and outboxed me but best believe if we do a third fight I'm going to get in the best shape of my life.
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"I thought I was going to feel stronger and better but next fight I admit I'm going to be more prepared. I was chasing him instead of cutting the rings. I felt like I couldn't throw my combinations."
Joshua came in over three stone lighter than Ruiz Jr, and used his speed to cruise to a points victory in Saudi Arabia.
All training camp, Ruiz looked to be faster and scarier than when he knocked Joshua out in New York in June.
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Ruiz Jr tried to shrug it off, saying: "I was already the same weight as the last fight this morning.
"I had to wait until almost 5pm to get on the scale, so I already had my breakfast, lunch and dinner. I also weighed in with my sombrero and pants on, so that's why I came in so heavy."
"It was a psychological thing as well."
Featured Image Credit:Topics: Andy Ruiz Jr, Anthony Joshua, Boxing
