Guðmundsson leaves with three years of eligibility remaining.
The Nittany Lions are set to be joined by Clemson, San Francisco, and Fordham.
Olu Fashanu to New Orleans is a popular pick in recent mock drafts.
Isaac led the Nittany Lions with 7.5 sacks last season.
Kyle Lehman and TJ Malone each earned weekly awards from the Big Ten on Tuesday.
A large group joined alum Paul Johnson on his trek though State College during his run from Los Angeles to New York City.