The Detroit Tigers have extended invitations to the Toledo Mud Hens, the Erie Seawolves, the West Michigan Whitecaps, and the Lakeland Flying Tigers to remain as affiliated minor league clubs for the 2021 season. The Norwich Sea Unicorns, formerly the Connecticut Tigers, did not receive an invitation.
Major League Baseball teams have sent out invitations to 119 minor league clubs to be affiliates for the 2021 season. MLB plans to have 120 affiliates, four per club and one each at the Triple-A, Double-A, High-A and Low-A levels, plus rookie league teams that are owned by the MLB clubs themselves.