Release clauses are pay the entire sum in 1 payment.
Do you honestly think they can pay that cost up front for 1 player? Their M.O. lately seems to be free agents as they're already a BILLION + in debt and can't pay huge transfer fees.
So yes it could happen, but they'd have to massively sell players first.
PSG seems much more likely or Real Madrid or maybe the Saudis. But I'd still put down a 50% chance that he will just end up staying till the end of his contract, earning a big salary and going back to Benefica since that's what he really wants.. to go HOME!