Google's planned flotation has been delayed for at least a day as paperwork required for its shares to be sold has yet to be approved by regulators.
The search engine firm's estimated $3.3bn (£1.79bn) market launch had been expected to get the nod by Tuesday.
However, the Securities and Exchange Commission did not give the all clear as expected to allow Google to start issuing shares and then begin trading.
The SEC gave no reason for the apparent delay to the highly anticipated IPO.
Some observers said they now expect the go-ahead to be given after Wall Street closes on Wednesday.
"We have always had to be patient, and we will just have to wait one more day," said Barry Randall, who manages technology stocks at US Bancorp Asset Management.
Once the SEC gives its approval, Google will stop accepting bids for its shares and could start issuing stock within a matter of hours.
Google revealed on Monday that the US stock market watchdog had launched an informal inquiry into its failure to register shares given to employees.
There was no indication that the inquiry would delay the firm's market debut.
Google declined to comment on the probe.
It centres on Google's failure to register 23 million shares and 5.6 million share options which it offered to employees and consultants, a possible breach of US stock market rules.
Google could face fines if the SEC finds that the share issue was contrary to stock market regulations.
The company has offered to buy back the shares, albeit at a lower price than they are expected to reach when traded on the stock market.
There is no guarantee that the holders of the shares will accept the buyback offer. Some may choose to sue the company instead.
A 'Dutch auction' aimed at setting the price of Google shares is already under way.
The auction is designed to give small investors a better chance of getting their hands on the shares that have been made available.
Potential investors are asked to specify both the price they are willing to pay, and the number of shares they want.
The bids are placed in order, starting with those offering the highest price. The allocators work down the list from the top, allotting each bid in turn the shares it requests, until all the shares available have been accounted for.
The lowest successful bid then becomes the issue price, and the flotation can begin.
Analysts estimate that the firm could be priced at between $108 and $135 a share, valuing it at $36bn (£19bn).
Google will trade on the technology-heavy Nasdaq exchange.