The Los Angeles Times reports that the actor will play a "bully from Marshall's past" in an upcoming episode.
The instalment will see Strong reunited with Mother star Alyson Hannigan, who previously played Willow Rosenberg on Buffy.
Hannigan's real-life husband Alexis Denisof will also reprise his role as news anchor Sandy Rivers in an episode expected to air on January 3.
When Robin (Cobie Smulders) lands a new dream job, Rivers is said to throw "a huge wrench in her plans".
Denisof also appeared on Buffy and its spinoff Angel as Wesley Wyndham-Pryce.
How I Met Your Mother continues on Mondays at 8/7c on CBS.