Kabuto said to tobi that he can nullify hasirama's power by the use of special drugs that he invented (see pic below)
He also said that he will not use this drugs to zetsu because it has a side effect to zetsu...





On the other hand naruto has a different version of special drugs on how to nullify hashirama's power (see pic below)
The white zetsu turn into trees after they were defeated by naruto..






If we're going back to what madara said about how to awaken the rinnegan
were,
rinnegan = senju power + uchiha power
in which,
senju power = hashirama's power
therefore,
without senju/hashirama's power there will be no rinnegan right? yes

So what will be naruto going to do to eliminate or prevent madara from using rinnegan? the answer is first he need to nullify hashirama's power in madara's chest... by how? by punching or a direct hit of rasengan to hashirama's face!!! (see pic below)





IMO when madara's chest become trees (like what happen to danzo's right arm) his senju power will suppressed and madara's rinnegan will be GONE... and madara's last option is to use his uchiha power...

Anyways I could also be wrong, what do you think?