James DeGale says he will "go back to the drawing board" after his shock defeat by American Caleb Truax at London's Copper Box Arena.
DeGale lost his IBF world super-middleweight title as Truax won 114-114 115-112 116-112 on the cards.
The Briton was as short as 1-100 with some bookmakers as he fought for the first time since January.
"There's something missing in the ring," said 31-year-old DeGale, who had shoulder surgery in July.
Truax, 34, offered constant pressure and rocked DeGale in the fifth as a stiff right drew gasps in the venue.
DeGale, timid for large parts, rallied late on but Truax took the title.
Speaking to BBC Radio 5 live after the fight, DeGale - who suffered his second professional defeat - added: "I honestly did [think I'd won], I've got to go back to the drawing board.
"My nose is blocked again, I've got to sort it out. The shoulder - I had serious reconstruction - there's no pain but I'll have to go back, have a look and see. I've probably rushed back to be honest, maybe I should have waited till next year."
He added: "I'm going to speak to Al Haymon [his boxing advisor] later, maybe I can get a rematch."
Truax, who extended his record to 29-3, said: "All week all I heard was who he's going to fight next. Well guess what? Those fights are mine now.
"I'd love to [fight in the UK again]. I'm staying until Wednesday - if anybody sees me, buy some pints."
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