diff --git a/CHANGELOG.md b/CHANGELOG.md
index 32320fdec6571..aa47dfe3c8bb4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -333,6 +333,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed `log_gpu_memory` metrics not being added to `logging` when nothing else is logged ([#8174](https://github.com/PyTorchLightning/pytorch-lightning/pull/8174))
 
 
+- Fixed a bug where calling `log` with a `Metric` instance would raise an error if it was a nested attribute of the model ([#8181](https://github.com/PyTorchLightning/pytorch-lightning/pull/8181))
+
 ## [1.3.7] - 2021-06-22
 
 - Fixed a bug where skipping an optimizer while using amp causes amp to trigger an assertion error ([#7975](https://github.com/PyTorchLightning/pytorch-lightning/pull/7975))
diff --git a/pytorch_lightning/core/lightning.py b/pytorch_lightning/core/lightning.py
index bf05b1f0772f0..ab8263bc8d4b5 100644
--- a/pytorch_lightning/core/lightning.py
+++ b/pytorch_lightning/core/lightning.py
@@ -375,7 +375,7 @@ def log(
                 # compute once
                 self._metric_attributes = {
                     id(module): name
-                    for name, module in self.named_children() if isinstance(module, Metric)
+                    for name, module in self.named_modules() if isinstance(module, Metric)
                 }
                 if not self._metric_attributes:
                     raise MisconfigurationException(
@@ -383,7 +383,7 @@ def log(
                         " You can fix this by setting an attribute for the metric in your `LightningModule`."
                     )
             # try to find the passed metric in the LightningModule
-            metric_attribute = self._metric_attributes.get(id(value))
+            metric_attribute = self._metric_attributes.get(id(value), None)
             if metric_attribute is None:
                 raise MisconfigurationException(
                     "Could not find the `LightningModule` attribute for the `torchmetrics.Metric` logged."
diff --git a/tests/metrics/test_metric_lightning.py b/tests/metrics/test_metric_lightning.py
index 8ce7f1050c6fe..5a20bc2475ffc 100644
--- a/tests/metrics/test_metric_lightning.py
+++ b/tests/metrics/test_metric_lightning.py
@@ -1,9 +1,27 @@
+# Copyright The PyTorch Lightning team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from re import escape
+
+import pytest
 import torch
+from torch import nn
 from torchmetrics import Metric as TMetric
 
 from pytorch_lightning import Trainer
 from pytorch_lightning.metrics import Metric as PLMetric
 from pytorch_lightning.metrics import MetricCollection
+from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from tests.helpers.boring_model import BoringModel
 
 
@@ -192,3 +210,78 @@ def training_epoch_end(self, outputs):
     logged = trainer.logged_metrics
     assert torch.allclose(torch.tensor(logged["SumMetric_epoch"]), model.sum)
     assert torch.allclose(torch.tensor(logged["DiffMetric_epoch"]), model.diff)
+
+
+def test_log_metric_no_attributes_raises(tmpdir):
+
+    class TestModel(BoringModel):
+
+        def training_step(self, *args):
+            metric = SumMetric()
+            self.log("foo", metric)
+
+    trainer = Trainer(default_root_dir=tmpdir, fast_dev_run=1)
+    model = TestModel()
+    with pytest.raises(MisconfigurationException, match="Could not find the `LightningModule` attribute"):
+        trainer.fit(model)
+
+
+def test_log_metrics_wrong_attributes_raises(tmpdir):
+
+    class TestModel(BoringModel):
+
+        def __init__(self):
+            super().__init__()
+
+            self.a_metric = SumMetric()
+
+        def training_step(self, *args):
+            metric = SumMetric()
+            self.log("foo", metric)
+
+    trainer = Trainer(default_root_dir=tmpdir, fast_dev_run=1)
+    model = TestModel()
+    with pytest.raises(MisconfigurationException, match=escape("where `name` is one of ['a_metric']")):
+        trainer.fit(model)
+
+
+def test_log_metric_dict(tmpdir):
+
+    class TestModel(BoringModel):
+
+        def __init__(self):
+            super().__init__()
+            self.metrics = nn.ModuleDict({'sum': SumMetric(), 'diff': DiffMetric()})
+            self.sum = 0.0
+            self.diff = 0.0
+
+        def training_step(self, batch, batch_idx):
+            x = batch
+            self.metrics['sum'](x.sum())
+            self.metrics['diff'](x.sum())
+            self.sum += x.sum()
+            self.diff -= x.sum()
+            self.log_dict({f'{k}_step': v for k, v in self.metrics.items()})
+            return self.step(x)
+
+        def training_epoch_end(self, outputs):
+            self.metrics['sum'].compute()
+            self.metrics['diff'].compute()
+            self.log_dict({f'{k}_epoch': v for k, v in self.metrics.items()})
+
+    model = TestModel()
+    model.val_dataloader = None
+
+    trainer = Trainer(
+        default_root_dir=tmpdir,
+        limit_train_batches=2,
+        limit_val_batches=2,
+        max_epochs=1,
+        log_every_n_steps=1,
+        weights_summary=None,
+    )
+    trainer.fit(model)
+
+    logged = trainer.logged_metrics
+    assert torch.allclose(torch.tensor(logged["sum_epoch"]), model.sum)
+    assert torch.allclose(torch.tensor(logged["diff_epoch"]), model.diff)