Truax, the 34-year-old American, was a 16-1 outsider to beat the former Olympic champion at London’s Copper Box Arena on Saturday night.
But DeGale, who was taken to hospital after the bruising encounter following a suspected broken nose, was no match for Truax and lost on a majority decision.
DeGale was making his comeback after nearly a year on the sidelines following shoulder surgery, and was expected to have despatched of Truax with a view to fighting long-term rival George Groves or Chris Eubank Jnr in an all-British mega fight next year.
But the 31-year-old’s career now hangs in the balance after losing his IBF super-middleweight title with Eubank Jnr describing his performance as “shameful” and Groves urging his long-term rival to hang up his gloves.
“I am devastated with my performance last night,” DeGale tweeted on Sunday. “I feel like I’ve let everyone down – myself, my family, friends and fans. I don’t want to be in any other position than No 1 so I am going to take some time out to reflect and make some decisions going forward.”
DeGale’s tweet would appear to suggest the Londoner, who shot to prominence after winning Olympic gold at the 2008 Beijing Games, is considering his future in the ring.
But Warren, who already has one eye on a rematch with Truax, believes DeGale will fight on.
“I don’t think he will retire,” Warren said. “You’ve got to be tough mentally, and if you had a bad day at the office, as James had, then you have got to push it to the back of your mind, learn from it, get back in the ring and show them what you are made of.
“It is not like he is a washed-up fighter. He is only 31 and he is still a young man. Of course it is a setback – any loss is a setback for a champion if you lose your title – but champions come back and win and we have seen a lot of fighters do that over the years.”
DeGale’s fourth defence of his title fell apart in the fifth round after Truax unleashed a number of fierce shots with his opponent up against the ropes. DeGale somehow survived the barrage, but headed to his corner bruised, bloodied and in deep trouble.
DeGale put up brave resistance to stay in the fight, but it was Truax who delivered the more telling shots, with two judges scoring the fight 115-112 and 116-112 in favour of the challenger.
“James got his tactics wrong,” Warren added. “I know what I am going to say when I see him. He might not want to hear it, and he might tell me to p*** off and mind my own business, but you can only say what you think.
“I went to the corner in the 10th round and said, ‘James, you are behind in this fight and you need to win these two rounds at least’. I jumped up in the last round and screamed at him: ‘James, you’ve got to knock him out.’ He looked at me quizzically.
“He could have won the fight, but he let the other fella make it his by being the aggressor and coming forward and that caught the eye of the judges.”
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