Last December, I wrote a Foolish book review about Sandy Weill's autobiography The Real Deal. Back in the 1980s, Weill set out to build a diversified and global financial empire. After a variety of transformative acquisitions, he accomplished the feat with the creation of Citigroup (NYSE:C). Despite the heft, the company has treaded water over the past few years and so has the stock. Now there are signs that major investors want to undo Weill's vision.

According to a filing with the SEC, Edward Lampert's ESL Investments disclosed a 15-million share stake in Citigroup, worth around $800 million. For a company with a market cap of $271 billion, it's really a bit trifling.

Yet it is highly symbolic. Lampert is one of the top hedge-fund managers, and some say he's the next Warren Buffett.

Over the years, Lampert has shown he's far from passive when it comes to putting his money to work. Just look at his efforts at Sears Holdings (NASDAQ:SHLD), where he sold non-core assets, cut costs, promoted managerial accountability, and had a laser-like focus on cash flows.

Citigroup's approach seems to be anti-Lampert. While it's true that the company is cutting costs, the measures are tepid. The goal is to realize savings of $4.6 billion over the next three years. Keep in mind that the company currently has about $52 billion in operating expenses.

My hunch is that Lampert wants something more radical, and that means breaking up the company. What are the synergies between investment banking and retail banking? I'm not sure, but Citi CEO Chuck Prince thinks they do exist.

With the strong stock prices in Goldman Sachs (NYSE:GS) and Morgan Stanley (NYSE:MS), it is not unreasonable to assume that a spinoff of Citigroup's investment bank would garner a nice premium. It would also have less bureaucracy and the incentives would be more aligned for employees.

So can Lampert make a change with such a low stock position? He can't do it alone, but this move is likely to encourage other hedge funds to buy up shares. Citigroup shareholder Saudi Prince Alwaleed bin Talal has also shown his disappointment with the company.

This is not to imply that there will be quick changes. In keeping with the Buffett philosophy, Lampert takes the long-term view. But I have a feeling he won't wait long before giving some advice to the lumbering Citigroup.

For further Foolishness:

Do you think you could pitch your favorite stock or ditch your least favorite one in less than 27 seconds? That's what we're doing over at Motley Fool CAPS. Check out our new stock videos.

Fool contributor Tom Taulli, author of The Complete M&A Handbook, does not own shares mentioned in this article. He is currently ranked 1,590 out of 24,619 rated players in CAPS.