But that's not the whole story. Of the roughly $3 decline in Yahoo's share price since the start of the year, only about $1.60 can be explained by Alibaba's slide. (That calculation can be made using Yahoo's own disclosures, which indicate the company holds about 0.393 shares of Alibaba for every one of its own shares.)
What about the remaining $1.40 decline? Yahoo shareholders interviewed by CNBC say it's partly the result of rumors and news reports last week—none of which have been borne out—suggesting Yahoo was pursuing shareholder-unfriendly acquisitions.
Shareholders are on pins and needles as they await the company's fourth-quarter earnings release on Jan. 27, by which time CEO Marissa Mayer has indicated she will announce a plan for divesting the Alibaba stake. The company has been under pressure since the fall from activist investor Starboard Value, which has advocated a tax-free spinoff of the company's stakes in Alibaba and Yahoo Japan, along with a potential merger of the core business with rival AOL.
Yahoo shareholders say they are worried about what Mayer is thinking as more time passes without an announcement from the company. One shareholder pointed out that it would require board approval to execute a tax-free spinoff of the Alibaba stake. If that board meeting has already occurred—which isn't clear—the company might have been obligated to make a public announcement.
Starboard may have added to the tension on Thursday, when it published a letter to the company expressing concern over a variety of issues, including rumors that Yahoo was looking for acquisitions. Starboard, AOL and Yahoo all declined to comment to CNBC.
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Starboard's letter also cited market chatter about Yahoo pursuing a so-called cash-rich split-off of its stakes in Alibaba and Yahoo Japan. Such a transaction would involve Alibaba or Yahoo Japan buying back the minority stakes from Yahoo with a combination of cash and an "active trade or business." Starboard said such a transaction is inferior to a tax-free spinoff for several reasons, namely that it may result in a lower valuation for the stakes and put cash in Yahoo's pocket that might be used in shareholder-unfriendly acquisitions.
Recently, some Yahoo investors have been more focused on the tax-free divestitures than any deal with AOL. Yahoo shareholders say they are effectively negotiating with Mayer and expect her to focus on the Alibaba stake first, followed by the Yahoo Japan stake and potentially a deal with AOL or another company. That said, some Yahoo shareholders including Starboard appear to be as keen as ever to merge the company with AOL.
Yahoo is technically allowed to disclose its plans for the Alibaba stake at any time. While Yahoo agreed to a one-year lockup period following the Chinese company's U.S. IPO in September, it is now free to disclose its intentions for the stake.
Until Yahoo shareholders get an answer, don't expect them to lose their jitters.
Disclosure: CNBC has a content-sharing partnership with Yahoo's finance site.