We've received around £27m from player sales so far this window, so even with Willian that £90m reduces to around £63m net spend. We can afford this because we've spent very little in net terms for several recent windows and we don't spend so much money on wages as some other clubs.
There are other factors too, such as shirt sponsorship deals that have again improved this summer, plus the extra TV money that all clubs will get this season (and for the next two after that).
However, IF RM come up with the fabled mega dosh then I'd expect Levy to take it. But behind the scenes RM have financial problems looming and there remain doubts that they actually can find the money except on a "never-never" instalment basis which Spurs won't accept.
Basically, Levy won't gamble on RM coming up with the goods. So if we're spending money now it's because we can afford it regardless.