There were no details on the suitor’s identity, although speculation is already running rampant that this could be the first game-changing move for Satya Nadella since taking over last year as CEO of Microsoft (MSFT). It’s also worth remembering that prior to being named CEO, Nadella led Azure, Microsoft’s cloud business.

A deal for Salesforce (CRM), whose market value is approaching $50 billion, would be among the largest tech acquisitions ever. Microsoft, worth just over $400 billion, is one of the few companies that could pull off such a deal, with $95 billion in cash (although much of that is offshore). From a strategic perspective, Microsoft’s customer relationship software offering that competes with Salesforce is considered to be an inferior product with a weaker market position.

What’s more, Microsoft and Salesforce have been increasingly chummy since Nadella became CEO. The two companies have an agreement to promote each other’s products, including a tie-in with Microsoft’s Office 365, the giant’s online version of its popular collection of productivity tools. In fact, Salesforce CEO and founder Marc Benioff has repeatedly and publicly lauded Nadella’s leadership, especially compared with Nadella’s predecessor, Steve Ballmer.

In an interview with Fortune in January, Benioff observed:

“Satya’s [been] talking about what he is trying to achieve with the company and how he wants to be more collaborative. So I decided to test him. I told him I wanted to hire one of his technologists as head of our infrastructure. What would be in it for Microsoft is the foundation of a partnership and give us more kind of ideas of things that we can do together. And he said okay. Now we’re learning about things that we could do with Microsoft’s file-management technologies and Office that we would never have known on our own.” Asked to describe the impact of the Ballmer-to-Nadella transition, Benioff said: “The other guy did not care about having a relationship with Salesforce. In fact he kind of did everything he could to not have a relationship with Salesforce.”

It’s unlikely Microsoft would buy Salesforce for its revenue. Instead, Nadella would consider the move a radical opportunity to shake up Microsoft’s culture by relocating the company’s headquarters to San Francisco and leaving behind some of Microsoft’s hidebound ways. Few Benioff observers expect the 50-year-old entrepreneur to relinquish control of his company. Then again, he gave up the CEO position at Salesforce once before, and he speaks frequently about the joy he gets from philanthropy.

A Microsoft spokesman declined to comment. Salesforce said in a statement: “We don’t comment on rumors.” One thing that’s certain is that Benioff and Nadella were together Tuesday night in San Francisco. Both attended a reception for CEOs that Microsoft hosted before a software developer’s conference Wednesday.

After Microsoft, the list of potential acquirers of Salesforce is short. Oracle (ORCL) is the most logical candidate, but the company runs its balance sheet conservatively. It did raise $10 billion in debt Wednesday, but many large tech companies, including Apple (AAPL), have been taking advantage of low rates to raise debt in order to finance buybacks and dividends without repatriating overseas cash. IBM (IBM) and SAP would make strategic fits for Salesforce, but neither has the huge cash reserves that Microsoft has, and SAP has been busy digesting its purchase of expense- and travel-management software maker Concur.

An even better fit for Salesforce would be Amazon (AMZN), which could combine its Amazon Web Services unit with Salesforce’s sales and marketing software products. But Amazon, which is barely profitable itself, isn’t likely to be able to afford to buy Salesforce. A deal this size for a company will such little cash flow is considered to be off limits for a private-equity transaction. Representatives of Oracle, SAP, Amazon, and IBM declined to comment. (Oracle will get another opportunity: It is hosting its first-ever media day Thursday at its headquarters in Redwood Shores, Calif., and its joint CEOs, Mark Hurd and Safra Catz, both are expected to take questions from journalists.)

Alternatively, if Salesforce has been approached as a buyout candidate and has retained bankers, it could turn the tables and become an acquirer itself. Two likely candidates would be Workday (WDAY), whose human-resources software complements Salesforce’s offerings, or Adobe (ADBE), increasingly a player in marketing software in competition with Salesforce.

The biggest head-scratcher in the purported buyout talks is why Salesforce would be willing to sell at all. “They are one of the most innovative companies in our industry,” says Brent Thill, an analyst with UBS who has followed enterprise software for years. “The platform [of third-party software developers] has been a big form of differentiation. They have the right pricing, the right go-to-market strategy, the right culture. Of all the companies I follow, they are the closest to being on autopilot. It’s really hard for them to screw up.”

And maybe Thill’s observation ultimately provides the rationale for a deal: Perhaps Salesforce is simply too tempting a target for the biggest software company of them all.

For more about Marc Benioff, watch this Fortune video:

(This story was updated with additional information)