Harmon was allegedly caught with 58 grams of marijuana inside a can of iced tea, three pipes with cannabis oil, a THC candy, and four glass containers with compressed marijuana that weighed 4.3 grams, Rapoport reported.
Harmon was not arrested, Rapoport added.
Harmon acknowledged the incident and apologized in an Instagram post Saturday evening.
Harmon, a Patriots third-round pick in 2013, started 21 regular-season and postseason games for New England over the past five years, logging 14 interceptions.
He could be subject to potential discipline by the NFL under the league's personal conduct policy.