Betfair, the betting exchange, has lost its finance director two weeks after appointing banking advisers to work on plans to float the business on the stock market.
Owen O'Donnell was appointed finance director in November 2003 and was granted options over 245,000 shares, vesting in 2008. He will leave Betfair at the end of next month.
In a short statement, chief executive Stephen Hill, who previously worked closely with Mr O'Donnell at Pearson, said: "Owen has made a significant contribution to Betfair's development during the past two years.
"We are grateful to him and wish him well in his future career."
His substantial share options package suggests Betfair had expected Mr O'Donnell to be with the company for some time, and certainly through any flotation process. It is not clear what value will now be put on his options, which are expected to crystallise on his departure.
The betting exchange group has appointed headhunters to look for a replacement. The company is thought to be seeking someone able to work with its banking advisers on flotation plans.
Goldman Sachs and Morgan Stanley were appointed earlier this month.
The company is thought to be considering plans to come to the stock market in the first three months of next year. It is expected to seek an investment multiple similar to listed international internet businesses, stressing the differences between Betfair and traditional bookmakers.
Betfair's claims to be capable of expanding beyond the UK are likely to be greatly enhanced if it can win a licence in another major gambling territory. It has been lobbying Australian state governments for several years and a decision from the Tasmanian premier is expected in December.
Meanwhile Betfair is thought to be struggling to convince the Treasury not to increase its tax burden in a wide-ranging review of betting duty.
It has quietly signalled that it could switch server and call centre operations to Malta in order to avoid too heavy a UK betting tax.
The chancellor is expected to clarify betting exchange tax treatment in his pre-budget report in November.
The Treasury struck a deal to lower the tax burden on betting shop bookmakers four years ago on condition that they repatriated their fast-growing offshore online divisions back to the UK.
Betfair does not want to let tensions with the Treasury overshadow its flotation plans and is expected to stress that the location of servers and call centres will have little or no bearing on the profitability of the business.