David Haye blamed a toe injury suffered in training for the points decision defeat by Wladimir Klitschko in their heavyweight unification clash.
Britain's Haye, 30, fought cautiously and went on to lose in Hamburg with scores of 117-109, 118-108 and 116-110.
He insisted those tactics were enforced by injury, however: "I might not have been at my best but I gave it as much as I could," he said.
"I couldn't push on my right leg. I broke my toe on my right foot."
He added: "I couldn't push off the right foot to throw the right hand.
"I thought adrenaline would get me through it but it was tough. It's incredibly frustrating. We were thinking about pulling out three weeks ago but we couldn't with all these great fans here.
"My plan was to win this fight but for whatever reason it wasn't meant to be today. It's frustrating because I'm so powerful, but I couldn't land many punches.
"I was trying to egg Wladimir on to come closer so I could land some punches, but he fought the smart fight.
"I've got a lot of respect for Wladimir and he's a great fighter. Everything that was said in the lead up was for him to come and get me so I could land my shots."
Boxing promoter Frank Warren told BBC Radio 5 live's Sportsweek programme that Haye was a "cry baby" for blaming his defeat on his injury.
"He shouldn't be in the fight if he had a broken toe. Why be a cry baby after the event? It's ridiculous," said Warren.
"When your title's on the line you've got to give your all and he just didn't do that.
"To talk about toes and whatever afterwards is just cry-baby stuff and I thought it was quite embarrassing. You'd think he'd be a bit more gracious in defeat."
Former WBF heavyweight champion Frank Bruno agreed that Haye should not have taken part in the contest.
"If he had a broken toe I would advise him to pull out because a broken toe is your balance and it works everything," said the 49-year-old Briton.
"You can't punch straight, you can't balance yourself, you can't even move. A broken toe's a serious thing.
"If you've got a broken toe your balance and everything goes, but he must know his business. If he fought with a broken toe he must be a very brave man."
Klitschko, 35, was as unimpressed with Haye's performance as he was with his pre-fight antics.
"I've been criticised by David Haye after the [Sultan] Ibragimov fight and it was the same with him after three rounds, he gave up on offence," said the champion.
"Instead he was fighting like all of my opponents. I would have loved to make him my 50th knockout.
"I wish I could prove I was the better man with a knockout out of David Haye. His behaviour before the fight was disgraceful to the sport of boxing."
The Klitschko family is now in possession of all of the major heavyweight belts, with Vitali holding the WBC title, and Wladimir added: "I would call us now undisputed heavyweight champions and I am sharing with him a beautiful moment in my life."
Haye himself has vowed to retire in October on his 31st birthday and was noncommittal on whether that would leave him time for one more fight. Trainer Adam Booth was more hopeful though that his charge would fight again.
BBC Radio 5 live summariser Steve Bunce was ringside in Hamburg and he paid tribute to Klitschko's performance.
"This has been one of the best performances from Klitschko," said Bunce.
"Haye will be crushed, he was chasing in the last round, it's a form of consolation, Haye's camp came up with a plan but by round four they worked out that there was nothing they can do. They found the Klitschko curse he was too big and just had too much for Haye."