diff --git a/app/interactors/add_group_stage_to_tournament.rb b/app/interactors/add_group_stage_to_tournament.rb
new file mode 100644
index 0000000..d8071f2
--- /dev/null
+++ b/app/interactors/add_group_stage_to_tournament.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+class AddGroupStageToTournament
+  include Interactor
+
+  def call
+    tournament = context.tournament
+    groups = context.groups
+    context.fail! if tournament.stages.size > 1
+    if (group_stage = GroupStageService.generate_group_stage(groups))
+      tournament.stages = [group_stage]
+      context.tournament = tournament
+    else
+      context.fail!
+    end
+  end
+end