Mastercard has said it expects to delay its $2.45bn (£1.4bn) share issue after news that chief executive Bob Selander has been treated for prostate cancer.
The share issue should now take place in the second quarter of 2006
It had been set to launch the initial public offering (IPO) before the end of March, but it should now be delayed until the second quarter of the year.
The US credit card giant's share issue is expected to be the largest IPO since Google listed on the Nasdaq in 2004.
Mr Selander, 54, has had successful surgery and is now working from home.
He expects to return to the office in early March.
In a letter to investors, Mr Selander said his doctor had told him "not to undertake a demanding travel schedule, such as a road show over the next couple of months".
This means it will not be possible for him to undertake a typical pre-IPO promotional tour at this stage.
MasterCard is planning to float up to 49% of the company, with the whole firm valued at about $5bn.
It first proposed the issue last August.