In Be Alert for the “Hybrid” Witness Editor-in-Chief of Daubert Online Patrick J. Kenny writes:
Courts do not agree on this point. Some hold that a hybrid witness who did not prepare an expert report may testify only as to those matters on which they are testifying as a fact witness. E.g., Bynum v. MVM, Inc., 241 F.R.D. 52, 54 (D.D.C. 2007) (holding that a treating physician “‘may describe what she has seen, describe and explain her diagnosis and the treatment she prescribed'” but without a Rule 26 report “‘a treating physician may not testify as to issues of causation, foreseeability, prognosis, and permanency.'” (further citations omitted)).
Other courts hold that a report under Rule 26 is not required if the witness’s proposed opinion testimony, regardless of its substance, arises solely from the witness’s personal knowledge. E.g., Martin v. CSX Transp., Inc., 215 F.R.D. 554, 557 (S.D. Ind. 2003) (“a physician ‘whose proposed opinion testimony will come from his knowledge acquired as a treating physician, is not someone from whom a Rule 26(a)(2)(B) report is required.'” (further citation omitted)).