diff --git a/src/ui/mixins/tree_manager.py b/src/ui/mixins/tree_manager.py
index b71a0f8..60333f6 100644
--- a/src/ui/mixins/tree_manager.py
+++ b/src/ui/mixins/tree_manager.py
@@ -593,6 +593,14 @@ class TreeManagerMixin:
                         xsl_id_str = "_".join(str(x) for x in node.id)
                         xml_item.setData(1, Qt.ItemDataRole.UserRole, xsl_id_str)
 
+                        # Prüfe ob XML-Datei existiert und deaktiviere Knoten falls nicht
+                        if hasattr(self, "project") and self.project:
+                            xml_abs_path = self.project.project_dir / xml.xml
+                            if not xml_abs_path.exists():
+                                xml_item.setDisabled(True)
+                                xml_item.setToolTip(0, f"XML-Datei nicht gefunden: {xml_abs_path}")
+                                logger.warning(f"XML-Datei nicht vorhanden: {xml_abs_path}")
+
                         item.addChild(xml_item)
 
                         # Speichere XML-Item für spätere Widget-Updates (Progress Bar, Icon)