diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 38c495e1dd0f3..0c98a779424bd 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -168,10 +168,6 @@ def _holder(self):
     def _consolidate_key(self):
         return (self._can_consolidate, self.dtype.name)
 
-    @property
-    def _is_single_block(self) -> bool:
-        return self.ndim == 1
-
     @property
     def is_view(self) -> bool:
         """ return a boolean if I am possibly a view """
@@ -259,7 +255,7 @@ def make_block_same_class(self, values, placement=None, ndim=None):
     def __repr__(self) -> str:
         # don't want to print out all of the items here
         name = type(self).__name__
-        if self._is_single_block:
+        if self.ndim == 1:
             result = f"{name}: {len(self)} dtype: {self.dtype}"
         else:
 
@@ -476,8 +472,7 @@ def downcast(self, dtypes=None):
 
         values = self.values
 
-        # single block handling
-        if self._is_single_block:
+        if self.ndim == 1:
 
             # try to cast all non-floats here
             if dtypes is None:
diff --git a/pandas/core/internals/managers.py b/pandas/core/internals/managers.py
index eaf59051205d6..6055a6205d286 100644
--- a/pandas/core/internals/managers.py
+++ b/pandas/core/internals/managers.py
@@ -220,16 +220,8 @@ def set_axis(self, axis: int, new_labels: Index) -> None:
 
     @property
     def _is_single_block(self) -> bool:
-        if self.ndim == 1:
-            return True
-
-        if len(self.blocks) != 1:
-            return False
-
-        blk = self.blocks[0]
-        return blk.mgr_locs.is_slice_like and blk.mgr_locs.as_slice == slice(
-            0, len(self), 1
-        )
+        # Assumes we are 2D; overriden by SingleBlockManager
+        return len(self.blocks) == 1
 
     def _rebuild_blknos_and_blklocs(self) -> None:
         """
@@ -1486,6 +1478,7 @@ class SingleBlockManager(BlockManager):
     _is_consolidated = True
     _known_consolidated = True
     __slots__ = ()
+    _is_single_block = True
 
     def __init__(
         self,