This rumor was started because Alonso was busy doing the rounds in Spa and was spotted at a few garages such as Ferrari and Red Bull Racing, which can only be seen as a courtesy call, rather than something serious. At the same time the sharp-eyed observers will have seen Felipe Massa visiting Toyota.

Alonso has a three year contract with Mclaren although his attempts to bribe Ron Dennis into making him number one has created a great deal of tension, its also worth remembering that Ferrari has another year to run on Massa's contract and Kimi's..... Its also worth noting that Massa is managed by Nicolas Todt - The Ferrari group manager Jean Todt's son as is another Todt Jr protege - Luca Filippi - who is now being mentioned as a next years Ferrari test driver

Obvious Ralf Schumi is yet to be resigned at Toyota and this leave a space available for a decent driver,it would be financially desirable to be number one in Toyota for Massa but also career suicide as they have not established the ability to win yet or mount a challenge for the title... Would he want to go there ?

Obviously selling Alonso's contract would free up some much needed cash for McLaren's fine however considering BMW have already attempted to secure Alonso for next year and failed, the assumption must be based on how poor the relationship is between Mclaren and Alonso...Winning the world championship can fix problems encountered over the year.
Having number 1 on your car brings a lot of media interest which Mclaren may need next year as they are not up the sharp end of the grid.

Guess only time will tell, I can't see it myself