From Day on Torts we learn that the "Ohio Supreme Court has ruled that a plaintiff in a legal malpractice case must prove the collectibility of damages"  The case is Paterek v. Peterson & Ibold, No 2006-1811 (Ohio June 18, 2008)

We’ve written about this in the past, both here and in the New York Law Journal.  The rule is split in New York.  In the 1st Department, the burden is on defendant.  In the remaining departments, the burden to plead and prove is on plaintiff.