As Microsoft and iCahn circle, it looks like Yahoo will almost certainly lose a major advertising contract with Bebo, dealing it yet another body blow.

The news emerged as AOL officially closed the $850 million acquisition of Bebo and laid out the next steps in its integration. It turns out that Yahoo’s current ad-deal with Bebo only covers the UK, Ireland and Australia. Prior to this development, Yahoo’s deal last September to sell most of the display ads on Bebo was one of its largest in Europe. But Bebo’s agreement with Yahoo runs until September 2009, so it is pretty unlikely to be renewed. After September Bebo will be free to use AOL’s Platform A ad network in the US and elsewhere, confirmed Joanna Shields, Bebo’s chief executive and head of the new People Networks division.

Make that highly likely – this was the whole point of the Bebo buyout in the first place. Put it this way, do you really think AOL would let Bebo stay in the Yahoo fold with everything that’s going on?

And this is Yahoo’s only advertising relationship with a big social network, since Google has MySpace (ok, and Orkut of course) and Microsoft has Facebook. Queue more gnashing of teeth at Yahoo…