You can sue him for post-petition, but might sue for pre-petitio

Pre-petition debt is dischargeable, and post-petition debt is NON-dischargeable.  However, during bankcruptcy the tenant might have to assume the lease in order to stay in it.  Check his bankcruptcy papers. 

http://www.nolo.com/legal-encyclopedia/post-petition-debts-chapter-7-bankruptcy.html
See Lease section. 

So, yes, you can sue him for post-petition rents, mabye also pre-petition rent.