Also, how much players they can buy in one transfer summer? He already spent 300million, if he doesn't sell someone, how can buy more expensive players and stay in FFP? Plus he asking too much money for his players even if they don't play on the top level.
You have to remember that Real Madrid have not been spending so much for so seasons now and as seen in the previous transfers, they have been offloading players too at fair good prices.
So I am a pretty sure a couple of players will be offloaded and believe me they won't be cheap either so FFP will just be fine. I know Papa Perez knows what he's doing

That being said, Real Madrid had landed another new signing
Real Madrid confirm 48 million Mendy transfer
Lyon's Ferland Mendy has become Real Madrid's latest summer signing, joining the Blancos in a deal worth an initial 48 million (£42.7m/$54m)
Now, after spending heavily on bolstering the Blanco forward line with the Jovic and Hazard moves, Madrid have turned their attention on defence once again, bringing in the highly rated left-back on a six-year contract as the presumed heir to ageing Brazil legend Marcelo.
"Mendy will be presented on Wednesday June 19, at 1pm, in the Estadio Santiago Bernabeu."
According to Lyon, the sale was negotiated for the sum of 48m plus a further 5m in future bonuses.
Source: https://www.goal.com/en/news/real-madrid-confirm-48-million-mendy-transfer/Real Madrid will be compliant of FFP rules once their buying ends, theyll sell their top players and balance their books. The rebuilding has began at Real Madrid and once these players understand each other theyll be unstoppable, now all they need to do is to buy the final player Pogba. Manchester United are playing hardball with them but I expect Pogba will push for the transfer, and leave Manchester United for good.