A variety of circumstances can arise that would preclude an expert witness from testifying at trial. Experts tend to get excluded in federal court for one of two reasons: either the witness disclosure does not comply with the requirements under the Federal Rules of Civil Procedure, or the expert fails to meet the standards for admissibility set forth in the Federal Rules of Evidence. At times, more unique circumstances arise that can prevent an expert witness from testifying. In Noffsinger v. Valspar Corp., the retained expert witness died prior to trial. No. 09 C 916, 2013 U.S. Dist. LEXIS 203349 (N.D. Ill. Jan. 4, 2013).[1] In another case, an expert witness experienced a serious personal health crisis and could no longer testify. Dunkin’ Donuts Inc. v. N.A.S.T., No. 02 C 1272, 2005 U.S. Dist. LEXIS 16703 (N.D. Ill. Aug. 10, 2005). The expert witness in Vincent v. Omniflight Helicopters Inc., chose to withdraw when he was proven to have provided false information in his report. No. 08-C-0572, 2009 U.S. Dist. LEXIS 117966 (E.D. Wis. Nov. 24, 2009).

When faced with such a circumstance, the party whose expert is unavailable should file a motion to substitute their witness. The Federal Rules of Civil Procedure do not expressly dictate the standard the court should use in assessing a motion for expert substitution. District courts in the Seventh Circuit have used two different approaches when presented with a motion to substitute. The Northern District of Indiana treated the motion as a request to amend the scheduling order under Rule 16(b) in Lincoln Nat’l Life Ins. Co. v. Transamerica Fin. Life Ins. Co., No. 1:04-CV-396, 2010 U.S. Dist. LEXIS 103744 (N.D. Ind. Sep. 30, 2010). The expert witness in that case had recently been sentenced to fifteen months in federal prison and would no longer be able to participate in the trial. Rule 16(b)(4) provides that “[a] schedule may be modified only for good cause and with the judge’s consent.” Fed. R. Civ. P. 16(b)(4). When considering whether good cause exists, district courts primarily consider the diligence of the party seeking amendment. J.F. by Sifuentes v. Abbott Labs., Inc., No. 14- CV-847, 2017 U.S. Dist. LEXIS 37197 (S.D. Ill. Mar. 15, 2017).

Other courts have construed a motion to substitute as an untimely designation under Rule 26(a) and analyze whether to exclude the substitute expert as a discovery violation under Rule 37(c). The Northern District of Illinois took this approach in Assaf v. Cottrell, where a conflict arose due to the expert’s dual association with the parties, and a substitute expert witness was required. No. 10 CV 0085, 2012 U.S. Dist. LEXIS 9243 (N.D. Ill. Jan. 26, 2012). Rule 37(c)(1) provides: “If a party fails to provide information or identify a witness as required by Rule 26(a) or (e), the party is not allowed to use that information or witness to supply evidence on a motion, at a hearing, or at a trial, unless the failure was substantially justified or harmless.” In assessing whether the failure to comply with Rule 26(a) is justified or harmless, courts typically employ the four-factor test that was utilized in Assaf. Courts consider (1) the unfair surprise or prejudice to the opposing party; (2) the offending party’s opportunity to cure such prejudice; (3) the likelihood of trial disruption; and (4) any bad faith motivation on the offending party’s disclosure.

District courts disagree as to whether the Rule 16(b)(4) and Rule 37(c)(1) standards are coexistent. Compare J.F. by Sifuentes, 2017 U.S. Dist. LEXIS 37197 at 2 (finding the court need not determine whether any distinctions between the two rules are ones of semantics or substance), with Carlson v. Fewins, No. 1:08-CV-1991, 2016 U.S. Dist. LEXIS 183080 (W.D. Mich. Oct. 19, 2016) (“The two rules impose different burdens on the moving party.”). The underlying consideration, regardless of whether the court analyzes the substitution under Rule 16(b)(4) or 37(c)(1), is to ensure that the substitute expert witness is not a superior witness. Substituting a new witness does not provide an opportunity to escape from the concessions or admissions of the original expert. See J.F. by Sifuentes,2017 U.S. Dist. LEXIS 37197 at 3 (holding that the unavailability of a prior expert did not grant the moving party “carte blanche to generate new theories after several years of litigation”). While the substitute is not expected to parrot every opinion set forth by the prior expert or state an opinion with which he does not agree, a substitute expert’s testimony is generally restricted to the same subject matter as the original expert. Lincoln Nat’l, 2010 U.S. Dist. LEXIS 103744 at 3. When seeking an expert substitution, attorneys should find an expert who has a similar area of expertise as the original expert and expect the scope of the new expert’s testimony to be limited accordingly.