diff --git a/odoo/modules/module.py b/odoo/modules/module.py
index 9a2f7fcdbdd..d1740f7d045 100644
--- a/odoo/modules/module.py
+++ b/odoo/modules/module.py
@@ -316,8 +316,16 @@ def module_manifest(path):
     if not path:
         return None
     for manifest_name in MANIFEST_NAMES:
-        if os.path.isfile(opj(path, manifest_name)):
-            return opj(path, manifest_name)
+        candidate = opj(path, manifest_name)
+        if os.path.isfile(candidate):
+            if manifest_name == '__openerp__.py':
+                warnings.warn(
+                    "__openerp__.py manifests are deprecated since 17.0, "
+                    f"rename {candidate!r} to __manifest__.py "
+                    "(valid since 10.0)",
+                    category=DeprecationWarning
+                )
+            return candidate
 
 def get_module_root(path):
     """