diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index 6362f11a3e032..19e51d05feb92 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -1896,7 +1896,7 @@ def pre_processor(vals: np.ndarray) -> Tuple[np.ndarray, Optional[Type]]:
                 inference = np.int64
             elif is_datetime64_dtype(vals):
                 inference = "datetime64[ns]"
-                vals = vals.astype(np.float)
+                vals = np.asarray(vals).astype(np.float)
 
             return vals, inference
 
@@ -2271,7 +2271,7 @@ def _get_cythonized_result(
 
         for idx, obj in enumerate(self._iterate_slices()):
             name = obj.name
-            values = obj._data._values
+            values = obj._values
 
             if aggregate:
                 result_sz = ngroups
diff --git a/pandas/core/internals/managers.py b/pandas/core/internals/managers.py
index 3a7ab98ea6baf..88cefd3ebfebf 100644
--- a/pandas/core/internals/managers.py
+++ b/pandas/core/internals/managers.py
@@ -1552,10 +1552,6 @@ def _post_setstate(self):
     def _block(self) -> Block:
         return self.blocks[0]
 
-    @property
-    def _values(self):
-        return self._block.values
-
     @property
     def _blknos(self):
         """ compat with BlockManager """