In a general sessions tort case, a defendant must notify the plaintiff and the clerk if he or she thinks that fault should be shared or that another is solely at fault. Tenn. Code. Ann. § 16-15-735. Here's a link to statute: http://www.michie.com/
A defendant must also identify the allegedly at-fault party sufficiently so that a plaintiff may serve process on him or her. Brown v. Wal-Mart Discount Cities, 12 S.W.3d 785, 789 (Tenn. 2000).
How do you deal with a defendant's attempt to shift blame improperly (i.e., by not identifying the other at-fault party) in a general sessions court tort case? File a motion to strike and cite Brown.
Good luck.