Under Ohio law, a privilege log must at least "state that communications were made between attorney and client for the purpose of procuring legal advice or representation." Cargotec, Inc. v. Westchester Fire Ins. Co., 155 Ohio App.
Attorney-client privilege is codified in Ohio at R.C. 2317.02(A). This statute states that an attorney shall not testify without express consent of the client, or, in the case of a deceased client, the express consent of the surviving spouse or estate fiduciary.
Ohio Revised Code § 2317.02 states that an attorney may not testify concerning communications made to the attorney by the client, except under specific circumstances. The statute covers mostly testimonial disclosures and anything not covered by the statute is governed by the common-law privilege.
Rule 8.3 requires a lawyer to report "unprivileged knowledge of a violation of the Ohio Rules of Professional Conduct that raises a question as to any lawyer's honesty, trustworthiness, or fitness as a lawyer in other respects." Thus, there are two triggers to a lawyer's reporting duty under Rule 8.3.
This situation would breach Rule 1.9, which prohibits a lawyer from representing a client in a matter substantially related to one in which they had previously represented another client. In this case, the attorney would possess confidential information from the prior representation that could harm the current client.