diff --git a/lib/crewai/src/crewai/mcp/client.py b/lib/crewai/src/crewai/mcp/client.py
index f25a77112..b1c1cc8b0 100644
--- a/lib/crewai/src/crewai/mcp/client.py
+++ b/lib/crewai/src/crewai/mcp/client.py
@@ -461,14 +461,17 @@ class MCPClient:
         arguments = arguments or {}
         cleaned_arguments = self._clean_tool_arguments(arguments)
 
-        # Sign the outgoing message when a security manager is present
+        # Sign the outgoing message when a security manager is present.
+        # We use a shallow copy of cleaned_arguments inside the message dict
+        # so that storing the envelope back into cleaned_arguments does not
+        # create a circular reference (envelope -> message -> params -> arguments).
         if self.security_manager is not None:
             message = {
                 "jsonrpc": "2.0",
                 "method": "tools/call",
                 "params": {
                     "name": tool_name,
-                    "arguments": cleaned_arguments,
+                    "arguments": dict(cleaned_arguments),
                 },
             }
             signed_envelope = self.security_manager.sign_message(message)
diff --git a/lib/crewai/tests/mcp/test_mcp_security.py b/lib/crewai/tests/mcp/test_mcp_security.py
index 8ab7198e4..33de4b3f1 100644
--- a/lib/crewai/tests/mcp/test_mcp_security.py
+++ b/lib/crewai/tests/mcp/test_mcp_security.py
@@ -484,7 +484,7 @@ class TestToolResolverSecurityIntegration:
                 backstory="Test backstory",
                 mcps=[http_config],
             )
-            tools = agent.get_mcp_tools([http_config])
+            agent.get_mcp_tools([http_config])
 
             call_kwargs = mock_client_class.call_args.kwargs
             assert call_kwargs.get("security_manager") is None