diff --git a/changelogs/fragments/12124-redfish-setmanagernic-keyerror.yml b/changelogs/fragments/12124-redfish-setmanagernic-keyerror.yml
new file mode 100644
index 0000000000..2710cb1b84
--- /dev/null
+++ b/changelogs/fragments/12124-redfish-setmanagernic-keyerror.yml
@@ -0,0 +1,4 @@
+bugfixes:
+  - "redfish_config - fix ``KeyError: 'ret'`` when ``SetManagerNic`` cannot find a matching NIC
+    (https://github.com/ansible-collections/community.general/issues/5892,
+    https://github.com/ansible-collections/community.general/pull/12124)."
diff --git a/plugins/module_utils/redfish_utils.py b/plugins/module_utils/redfish_utils.py
index 32033e0df7..46b4923c07 100644
--- a/plugins/module_utils/redfish_utils.py
+++ b/plugins/module_utils/redfish_utils.py
@@ -3685,7 +3685,7 @@ class RedfishUtils:
         nic_info["ethernet_setting"] = target_ethernet_current_setting
 
         if target_ethernet_uri is None:
-            return {}
+            return {"ret": False, "msg": f"Manager NIC with address '{nic_addr}' not found"}
         else:
             return nic_info