Mikkel Kessler has claimed he peaked too soon in training before his rematch with Carl Froch.
Kessler suffered a points defeat against Froch in May and the Dane has been reflecting on their thrilling fight for Ringside - Froch-Kessler Special.
The Viking Warrior made a sluggish start to the super-middleweight unification clash and Froch's relentless assault earned him the verdict and Kessler's WBA title.
Kessler had edged out the Cobra on points in their gruelling first battle in 2010, but he struggled to last the pace during the return bout at London's 02 Arena.
He believes his preparations had been perfect until he suffered fatigue while sparring with British duo Nathan Cleverly and George Groves.
"I trained with Cleverly, Groves, I had a guy from Sweden called (Erik) Skoglund over," he told Ringside.
"I was training Monday, Wednesday and Friday and sparring. I think I had one of the best weeks of my career. I was moving, punching, everything.
"I was surprised, you know. I'm in the best shape ever! Nobody can beat me now it's impossible, so I had those three sparring rounds, good against Groves, good against Cleverly, first time I sparred them.
"I think I had one day off, Sunday, and then I went down for training on Monday, trained good Monday, and then I had Cleverly for about 10 rounds, less, and one 10-rounder.
"Went good the first four rounds, and then I started to get tired, very tired. I hold on for the 10 rounds and then Cleverly, he was coming at me, he was good, and was doing a really good job.
"But I was so tired I couldn't put it together, I couldn't punch and said: 'what's wrong?'"
Having studied footage of the fight, Kessler is certain his intense training was to blame for his laboured performance.
Froch appeared to be hurt in the closing stages of the bout, but Kessler insists he did not have enough strength to finish off his rival.
"Maybe I trained too hard and didn't get too much break and it was a big mistake for me," added Kessler.
"When I watched the fight after - with my trainer and my manager - I hit about under half of my punches. Under half of what I did in my first fight.
"I had him almost out in the 11th round and I couldn't finish it. I couldn't, I was too tired. I couldn't finish him and I couldn't finish in the 12th in the last minute. In the first fight I was the finisher, you know?
"But here it was, Carl was the finisher, that's why he did a good job Carl and no excuses here, but I peaked too much and that's what happened."
Both fighters reflect on the fight and re-live it round-by-round on Ringside - Froch-Kessler Special on 6pm, Thursday, Sky Sports 4.