Lions head coach Jim Caldwell had sent Mosley home on the day before the team's game in London versus the Atlanta Falcons and suspended him "for conduct detrimental to the team and a violation of team rules."
Mortensen reports that hotel security staff discovered the marijuana in Mosley's London hotel room after the defensive tackle disabled a smoke alarm in his room.
Mosley and the NFLPA have filed a grievance against the suspension and the pay Mosley has lost because of it, according to Mortensen. The union is arguing that a marijuana violation should fall under the NFL's substance abuse policy.
Mosley, a sixth-round draft pick out of Missouri, had played every game this season before the suspension, recording 2.5 sacks and one forced fumble.
The Lions (6-2) have a bye this weekend before hosting the Miami Dolphins on Nov. 9.
- Molly Geary