Bruce kept the Latics in the Premier League, while Birmingham were relegated to the Championship under his successor Alex McLeish.
"We thought that if we got involved in the club at least for some time, then we could take over and guarantee that nothing will go wrong," added Yu, who is chief operating officer of Yeung's investment company Grandtop International Holdings.
"But then when an article appeared in a Birmingham match programme saying that Mr Sullivan would not deal with Mr Yeung, it made us feel disappointed because it was not even close to the so-called deadline to buy the club outright.
"We have been very polite but they have been quite unreasonable. We didn't ask for anything nor have we done anything to hurt the club."
Yeung had been set a deadline of 21 December 2007 to complete his buy-out, but the Blues released a statement to the Stock Exchange on 20 December to announce that discussions had been terminated.
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