Oracle ended Friday with its worst week on Wall Street in 25 years, falling 19 percent over five sessions as investors questioned whether the software company can finance the artificial-intelligence infrastructure it has promised to build for OpenAI without straining its balance sheet.

The slide capped a week in which Asian technology indexes tumbled, South Korea's Kospi tripped circuit breakers for the third time, and veteran investor Jeremy Grantham told CNBC that the U.S. stock market is now the most expensive in the country's history.

The Oracle math

Oracle shares dropped at least 2.6 percent each day this week, CNBC reported, the steepest weekly slide since a 20 percent plunge in August 2001 during the dot-com bust. The stock has now lost about 55 percent of its value since reaching a peak market capitalization of $900 billion in September.

The pressure traces to the balance sheet. Oracle was carrying about $130 billion in debt at the end of May, capital expenditures rose 162 percent to nearly $56 billion in fiscal 2026, and the company recorded negative free cash flow of almost $24 billion in the latest fiscal year. Earlier this month it said it plans to raise $40 billion through debt and equity in fiscal 2027, including a $20 billion share sale.

Most analysts remain bullish. According to FactSet, 71 percent recommend buying the stock, the highest share in 15 years. Evercore analysts wrote in a Wednesday note that they expect "financing/leverage and the pace of equity issuance to remain the central investor debate near term, even as demand signals stay strong."

Co-founder Larry Ellison was absent from the company's most recent earnings call, leaving dual chief executives Clay Magouyrk and Mike Sicilia and recently appointed finance chief Hilary Maxson to face analysts. Maxson told investors the company would stay "focused on disciplined capital allocation, maintaining a strong balance sheet, and preserving our investment-grade credit rating."

Asia takes the cue

South Korea's Kospi was halted for 20 minutes Friday after falling 8 percent and closed 5.8 percent lower, the third circuit-breaker trip this week and the fifth this year, the BBC reported. Japan's Nikkei 225 closed more than 4 percent lower as shares in technology investment firm SoftBank fell 12.5 percent. Markets in Taiwan and mainland China also dropped sharply.

"The long term investment case for AI remains compelling, but investors are becoming far more selective about which companies can justify the valuations the market has assigned to them," David Makaryan, a senior partner at Alpha Pacific Group, told the BBC.

Grantham's number

On CNBC's "Squawk Box" Friday, Grantham, the co-founder of Boston-based GMO, cited the so-called Buffett indicator, which compares total U.S. equity value with GDP. "Based on the value of the stock market compared to GDP, with modifications, this is the most expensive market in American history," he said. The ratio is estimated at 235 percent, according to Longtermtrends.com. Warren Buffett has previously written that when it approaches 200 percent investors are "playing with fire."

Grantham conceded the timing of any decline was uncertain and acknowledged that a similar March 2024 warning was followed by further gains. He compared SpaceX, which carries a roughly $2 trillion valuation after its initial public offering, to Amazon, whose shares fell 92 percent after the dot-com bubble before the company "inherited the earth."

The other side

No bullish counterweight to Grantham appeared in today's wire-tier reporting. Oracle did not respond to CNBC's request for comment, and spokespeople for OpenAI were not quoted. The clearest defense came from inside the same Oracle coverage: Evercore's buy recommendation and the FactSet tally that nearly three-quarters of analysts still rate the stock a buy, evidence that the sell-side has not yet capitulated even as the share price has.

Oracle is pressing on with its data-center buildout, with new sites targeted for Michigan, New Mexico and Texas in 2027. Next week's earnings calendar will test how far the AI capital-spending debate has spread.