diff --git a/src/azure-cli/azure/cli/command_modules/acs/managed_cluster_decorator.py b/src/azure-cli/azure/cli/command_modules/acs/managed_cluster_decorator.py
index 6efebb3201c..e46511f1097 100644
--- a/src/azure-cli/azure/cli/command_modules/acs/managed_cluster_decorator.py
+++ b/src/azure-cli/azure/cli/command_modules/acs/managed_cluster_decorator.py
@@ -2366,13 +2366,21 @@ def get_sku_name(self) -> str:
                 skuName = CONST_MANAGED_CLUSTER_SKU_NAME_BASE
         return skuName
 
-    @staticmethod
-    def _raise_missing_vnet_subnet_for_outbound_type(outbound_type: str, sku_name: str) -> None:
+    def _raise_missing_vnet_subnet_for_outbound_type(self, outbound_type: str, sku_name: str) -> None:
         if outbound_type == CONST_OUTBOUND_TYPE_USER_DEFINED_ROUTING:
             subnet_requirement = "a route table with egress rules"
         else:
             subnet_requirement = "a NAT gateway with outbound ips"
 
+        if self.decorator_mode == DecoratorMode.UPDATE:
+            raise InvalidArgumentValueError(
+                f"Updating outbound type to {outbound_type} is only supported for clusters created with "
+                "--vnet-subnet-id. Clusters using an AKS-managed VNet can't be updated to this outbound type. "
+                "Please refer to "
+                "https://learn.microsoft.com/en-us/azure/aks/egress-outboundtype#updating-outboundtype-after-cluster-creation "  # pylint:disable=line-too-long
+                "for more details."
+            )
+
         if sku_name == CONST_MANAGED_CLUSTER_SKU_NAME_AUTOMATIC:
             raise RequiredArgumentMissingError(
                 "--vnet-subnet-id must be specified for {outbound_type}. For an Automatic cluster "
diff --git a/src/azure-cli/azure/cli/command_modules/acs/tests/latest/test_managed_cluster_decorator.py b/src/azure-cli/azure/cli/command_modules/acs/tests/latest/test_managed_cluster_decorator.py
index be04d278208..ab6a217e15a 100644
--- a/src/azure-cli/azure/cli/command_modules/acs/tests/latest/test_managed_cluster_decorator.py
+++ b/src/azure-cli/azure/cli/command_modules/acs/tests/latest/test_managed_cluster_decorator.py
@@ -2020,6 +2020,24 @@ def test_get_outbound_type(self):
         ctx_1.attach_mc(mc)
         self.assertEqual(ctx_1.get_outbound_type(), "test_outbound_type")
 
+        ctx_1_1 = AKSManagedClusterContext(
+            self.cmd,
+            AKSManagedClusterParamDict(
+                {
+                    "outbound_type": CONST_OUTBOUND_TYPE_USER_DEFINED_ROUTING,
+                }
+            ),
+            self.models,
+            DecoratorMode.UPDATE,
+        )
+        ctx_1_1.agentpool_context = mock.MagicMock()
+        ctx_1_1.agentpool_context.get_vnet_subnet_id.return_value = None
+        with self.assertRaisesRegex(
+            InvalidArgumentValueError,
+            "only supported for clusters created with --vnet-subnet-id",
+        ):
+            ctx_1_1.get_outbound_type()
+
         # invalid parameter
         ctx_2 = AKSManagedClusterContext(
             self.cmd,