Birmingham co-owner David Sullivan has claimed that Upson pleaded to be sold.
Upson said: “I think the words ‘insisted that he release me’ are a bit strong.
“We had a telephone conversation. I wanted to get a bit of clarification out of what was happening because I knew that he, ultimately, was the decision-maker.
“Not once did I say he must release me or demand to be released because I can’t control his decision.
“I expressed a will to want to speak to West Ham if they agreed a deal.
“I always maintained my 100% commitment to Birmingham City while I was there.
“I refused two new contracts so they were aware I wouldn’t sign a new deal and I think it ended up being a big decision with the offer they received and they decided it was a good offer.”