Here's my theory:
There's a quote on the CBS website:
"While looting the losing tribe's camp after a Reward Challenge, a visiting castaway makes a stunning confession. "
I think that Jon is going to loot Morgan. While he's there, he will tell the BIG LIE, which will be some kind of story about Rupert which will make the Morgan members think badly of him. Then, Jon may go back to Drake and tell some other version of the lie which will cast Rupert in a bad light to his own tribe members as well. This will all result in Rupert getting voted off this week, or as soon as the merge occurs.
Just the musings of my addled brain.