Citigroup (NYSE: C) recently revived advertising slogan is reassuring: "Citi never sleeps." The idea is that since it operates in 100 countries, there is always a Citi employee on the job. But even if you have 300,000 employees, a company can only survive if those people are doing the right things when they're on the job. If not, Citi might never sleep, but it could take a dirt nap.

Citi stock has lost half its value this week and, at $4.71, is down 92% from its September 2000 high of $57.50. Prince Alwaleed said it was dramatically undervalued -- and that was yesterday morning before it lost 26% of its value. I suggested yesterday that the Prince may have miscalculated. How so? If you think that value can be measured by comparing the stock price to potential earnings growth, then I think the Prince overestimated the earnings growth part . For instance, its global cards and consumer lending business makes up 67.3% of net revenues, and global cards shrank 40% in the third quarter.

Since the prince has so much of his diminishing wealth -- his investment fund was down 63% as of yesterday -- tied up in Citi stock, he may have decided that people's memory of his 1991 investment killing based on buying at split-adjusted $2.98 -- will draw in buyers. But things are different now. Citi has posted huge write-downs in four consecutive quarters of losses totaling $20 billion; nine of its investment funds have collapsed this year; it will lose money due to write-offs of consumer loans, commercial real estate, and mortgages; and it has trillions of exposure to derivatives and illiquid assets.

As a Citigroup (NYSE: C) shareholder I know that Saudi Prince Alwaleed bin Talal made a killing back in 1991 when he backed up the truck and bought shares of Citi at what was then a low price of $10 a share -- $2 adjusted for splits. He is no doubt unhappy with the 90% drop in the value of the stock since its September 2000 peak of $57.50. Now he's trying for a repeat of his previous success by boosting his share of Citi from 4% to 5%. Unfortunately, it won't work this time.

Alwaleed's stock holdings have plummeted. For example, his Riyadh-based Kingdom Holding Co. has lost 63%, wiping out $13 billion in value. Citigroup, his largest holding, has fallen by more than 75% since January 15, when Alwaleed increased his stake. His concept that Citi is dramatically undervalued does not hold much water. The reason for that is that given its complexity and exposure to derivatives, off balance sheet entities and Level 2 and 3 assets -- which total $36.8 trillion, $1.2 trillion, and $1,195 billion (88.6% of total assets) respectively -- Citi is impossible to value.

Meanwhile, the steps that Citi has taken are not going to be enough to help it survive. Sure it has raised $75 billion by selling assets and equity stakes since December and plans to cut 52,000 jobs. But Citi has only $98.6 billion in common equity, and unfortunately, an 8% decline in the value of those Level 2 and 3 assets will wipe that out. Things are not good for Citi and that does not bode well for Alwaleed or Citi's other shareholders.

Peter Cohan is President of Peter S. Cohan & Associates. He also teaches management at Babson College and edits The Cohan Letter. He owns Citigroup stock.

Citigroup (NYSE: C) may need more cash. The head of Dubai International Capital told Reuters that it would take "a lot more money" to rescue Citigroup following investments from Abu Dhabi, Kuwait and Saudi Arabia's Prince Alwaleed.

The statement has the benefit of probably being true. Citi is almost certainly faced with more subprime losses and its derivative holdings of credit cards and munis plus LBO paper could lead the bank to have to write-off billions more in losses from these.

The question is where will the big bank go. Sovereign funds may not have an appetite for putting up more capital. US private equity firms may find the deal too risky. Things may get bad enough that the Fed will have to step in and give Citi a huge loan to keep its balance sheet solid enough for the bank to remain solvent.

The "a lot more money" may come from taxpayers.

Douglas A. McIntyre is an editor at 247wallst.com