Yes, it is very possible because it is unlikely that Real Madrid will be willing to spend a lot of money to recruit Osimhen from Napoli because their target is Mbappe.
But the Mbappe transfer drama is very long and Real Madrid really need a striker to replace the position left by Benzema, this is a little difficult I think.
Napoli don't seem to want to let Osimhen go, that's why they set a high price. In my opinion, it's really not worth it for Real Madrid to sign him and I think it's better to wait and keep chasing Mbappe.
Since multiple teams are interested in signing him for the upcoming season Osimhen future at Napoli may be in doubt. Real Madrid might be one of those interested parties but it's doubtful that they would agree to pay the exorbitant asking price Napoli has set, especially given the chance to get a player like Mbappe from PSG for a comparable sum. Given the possibility of losing Mbappe to a free agency after the 2018-19 season, PSG might be more open to negotiating a deal for him at a price exceeding €100m. Osimhen contract still has some remaining time, hence Napoli is probably going to stand by their asking amount.