diff --git a/src/pip/_internal/resolution/resolvelib/provider.py b/src/pip/_internal/resolution/resolvelib/provider.py
index a1bab05a4..8ad1c65d3 100644
--- a/src/pip/_internal/resolution/resolvelib/provider.py
+++ b/src/pip/_internal/resolution/resolvelib/provider.py
@@ -43,7 +43,7 @@ class PipProvider(AbstractProvider):
         self._constraints = constraints
         self._ignore_dependencies = ignore_dependencies
         self._upgrade_strategy = upgrade_strategy
-        self.user_requested = user_requested
+        self._user_requested = user_requested
 
     def _sort_matches(self, matches):
         # type: (Iterable[Candidate]) -> Sequence[Candidate]
@@ -84,7 +84,7 @@ class PipProvider(AbstractProvider):
             if self._upgrade_strategy == "eager":
                 return True
             elif self._upgrade_strategy == "only-if-needed":
-                return (name in self.user_requested)
+                return (name in self._user_requested)
             return False
 
         def sort_key(c):