Can A Landlord Sue For Back Rent Without A Lease Agreement?

When you rented the property I'm sure the landlord had to have made some verbal agreement if there wasn't a written one. Yes, you can be sued and especially if he has duplicate receipts of your payments but it all depends upon the judge what the outcome of this case would be.

Depends on the state and what mood the judge is in. If a verbal agreement (which you agreed to when you resided there) was in place, then yes, I believe they can.