My understanding of this, having never been in the situation, is that you need to be below 500k in the red on the economic update two weeks from yesterday. So you can play your final. You do need to sell player(s) before the update so make sure you list him (or them) on the thursday before the final so that they sell on sunday. Any bids on players would count in your economic update but since many people leave it late to bid its safer to make sure they sell on sunday.
Its important to also consider that any losses you make in the next two weeks will also have to be covered in order to put you under 500k.