I'd bet 15-20 to make it look like you're trying to block for a cheap river club. If he has something like AK, he'll probably raise you here, depending on the size of that raise I'd probably call again and pray that another club doesn't fall on the river to kill your action and then lead into him for a reasonable amount on the river. Of course you could be really lucky and he could have something like
![The King of Spades [Ks]](https://www.pofex.com/images/smilies/Ks.gif)
and then you probably have a pretty decent chance at getting all his money.