We've some odd rumoured departures so far this summer, but the one with the most legs has been the supposed sale of Kevin de Bruyne to Borussia Dortmund. And that's mostly because they won't shut up about it:
Der Spieler möchte zu uns. Das Heft des Handelns liegt da aber nicht in unserer Hand.
-Michael Zorc, BVB sporting director. Source: WAZ.
Google translating that gives you something like '[de Bruyne] wants to join us, but it is not in our hands'. And that's annoying. I don't know what de Bruyne wants, but publicly commenting on players under contract with different clubs is an odd move by Zorc. One hopes that he doesn't actually know what the player wants, given that de Bruyne's under contract with Chelsea through 2017 and would therefore require permission to talk to.
Anyway, whether or not de Bruyne wants out, it doesn't really matter. If Jose Mourinho and Chelsea want to keep him, they'll keep him. Players under long-term deals have zero leverage, and de Bruyne's value to other sides will only go up, as long as he's getting reasonable playing time. Coincidentally, selling him later is actually more beneficial under FFP rules than dumping him now. There is no sane reason to hand de Bruyne over to BVB this summer. Why won't this rumour die?