Mr McCann, as has been already reported, has sued Bank of America – now the owner of Merrill Lynch – seeking to lift the clause in various Merrill agreements so that he can work for a rival. However, BoA is arguing that Mr McCann must stay in his job through January 2010.

When BoA bought Merrill Lynch in a deal that was completed in January this year, it created the world’s biggest wealth management firm by size of assets. The firm is still a predominantly domestic US player, however, while UBS is arguably the world’s biggest international wealth manager.

A report by Reuters said that in a court filing on Tuesday this week, Mr McCann contended that he gave written notice on 5 January that he would resign and that Bank of America accepted his reason for leaving.

He said the bank rescinded its acceptance the following month, fired him effective 30 January, 2009, and won't let him take a job with a rival until a year after the firing.

"I face the likelihood of missing out on what I believe is a 'once in a lifetime' opportunity," he was quoted as saying. "At age 51, given the recent contraction of the financial industry and the scarcity of positions at the very senior level that are appropriate for me, I may never have a job opportunity like this again."

Bank of America, in court papers filed on Saturday, said Mr McCann is "intimately familiar" with its long-term strategic plans and that it would lose plenty of business if he went to work for a rival.

"At a competitor, McCann could and likely would act as a 'magnet' to attract top talent and important clients and business partners away," the bank said, according to Reuters. "The potential damage to Bank of America should this occur is incalculable."

In August, Bank of America hired Sallie Krawcheck, the former chief financial officer and wealth management chief of Citigroup, to run the combined brokerage of Bank of America and Merrill Lynch.