Yahoo (NSDQ: YHOO) stock crept up slightly on various European markets on Tuesday, after plummeting as much as 12.9 percent Monday following Microsoft’s (NSDQ: MSFT) cancellation of its acquisition bid. YHOO lists several stocks in Switzerland and Germany, where it gained nearly 10 percent. Its biggest European listing, in Frankfurt, was up by just 6.4 percent, however. Investors appeared more undecided on MSFT - up by over five percent in Amsterdam, where it keeps a very small number of shares, but down by as much as 4.49 percent in Berlin, its most voluminous European market. Though each European listing is many times smaller than each company’s core Nasdaq ticker, observers will be watching for any cross-market mimicking of investor behaviour.

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As we wrote when Microsoft made its offer in February, MicroHoo would have acquired Yahoo’s display ad deal with Bebo, but would find it very difficult to take search traffic from Google’s (NSDQ: GOOG) circa-80 percent European share and would have faced intense antitrust hurdles from the European Commission. What’s changed since then - Yahoo is retrenching in Europe, moving its senior managers from London to Geneva, while it’s also likely to lose its Bebo deal to the social net’s new owner, AOL.

What hasn’t changed - the EC challenge. This is the same European Commission - in competition commissioner Neelie Kroes - that in February slapped MS with a record 899 million euro (now £707 million) antitrust fine - the latest in a long list of MS-EU run-ins (another is ongoing). So if, as has been suggested, it’s really not over between Ballmer and Yang, Europe may yet require concessions wide-ranging enough to negate some of the original deal’s promise.