diff --git a/pymongo/asynchronous/mongo_client.py b/pymongo/asynchronous/mongo_client.py
index 754b8325ed..43dbd49f76 100644
--- a/pymongo/asynchronous/mongo_client.py
+++ b/pymongo/asynchronous/mongo_client.py
@@ -758,6 +758,7 @@ def __init__(
         self._host = host
         self._port = port
         self._topology: Topology = None  # type: ignore[assignment]
+        self._timeout: float | None = None
 
         # _pool_class, _monitor_class, and _condition_class are for deep
         # customization of PyMongo, e.g. Motor.
diff --git a/pymongo/synchronous/mongo_client.py b/pymongo/synchronous/mongo_client.py
index 1cedbfe1e2..2d8d6d730b 100644
--- a/pymongo/synchronous/mongo_client.py
+++ b/pymongo/synchronous/mongo_client.py
@@ -756,6 +756,7 @@ def __init__(
         self._host = host
         self._port = port
         self._topology: Topology = None  # type: ignore[assignment]
+        self._timeout: float | None = None
 
         # _pool_class, _monitor_class, and _condition_class are for deep
         # customization of PyMongo, e.g. Motor.