Duxbury added: "I would like to place on record our thanks to him for all his efforts and wish him the very best.
"I would also like to thank the fans for their patience and understanding during what has been a difficult time."
Gianfranco Zola took over as West Ham boss on 15 September, two days after what would turn out to be Ashton's last appearance in a Hammers shirt.
"It's a sad situation. He's very young, very talented, to see such a player having to retire is bad," said Zola.
Ashton will be missed - Zola
"I feel for him - and I feel for me because I wonder what it would have been like to have a player like him in my squad.
"He would have made a big difference for us and that is my regret."
The Italian added: "It was painful for me when I retired when I was 39 - he is only 26. Football is something you do with all your heart and passion so I leave it to you to imagine how he is feeling right now."
Former West Ham boss Harry Redknapp, who is now at Tottenham, told BBC Radio 5 live: "He was a good player, a terrific striker.
"He was in the England squad and looked like he was going to play in the forthcoming game when he picked up that injury. I wish him all the best in the future.
"It's really sad to see a young guy retire so early. He was a very good player."
Arsenal manager Arsene Wenger once contemplated signing the powerful striker when he was at Crewe.
"It is very said that Dean Ashton has to retire because I always thought he was a very intelligent and efficient player," said the Frenchman.
"I liked him personally as a player and as a personality on the pitch. It is sad, but in our job you depend on your health.
"The first quality of a good football player is that they have good health and we forget that many times."
Crewe manager Dario Gradi, who gave Ashton his professional debut at the age of 16, was not surprised by the announcement.
"We'd all seen it coming for a long time," Gradi said. "He's been injured for a while and I think that Dean was prepared for it.
"It's a shame for Dean but it's a great shame for England. They are crying out for a big striker and that is what he is.
"The saving grace for Dean is that he has had a bit of a career and will have made enough money not to have to work again."
Ashton's agent Darren Bossons declined to comment on reports that Ashton may look to take legal action against Shaun Wright-Phillips, who caused the striker's initial injury with a challenge during an England training session in August 2006.
And Professional Footballers' Association chief executive Gordon Taylor hopes Ashton does not go down that route.
Taylor said: "I hope it doesn't come to that because nobody would think that Shaun Wright-Phillips was a malicious player at all.
"At the moment we've been speaking to his [Ashton's] representatives and the situation is about looking to get proper compensation without discussing any player-v-player action."
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