diff --git a/public/course/editsection_form.php b/public/course/editsection_form.php
index 5263b02cc53..dd4031f4807 100644
--- a/public/course/editsection_form.php
+++ b/public/course/editsection_form.php
@@ -39,7 +39,18 @@ class editsection_form extends moodleform {
         $mform->setDefault('name', $sectioninfo->name);
         $mform->addRule('name', get_string('maximumchars', '', 1333), 'maxlength', 1333, 'client');
 
-        /// Prepare course and the editor
+        // Prepare course and the editor.
+
+        if ($sectioninfo->is_delegated()) {
+            // Show a warning that subsection descriptions will be discontinued.
+            $warning = $OUTPUT->notification(
+                message: get_string('subsectiondescriptionwarning', 'course'),
+                type: \core\output\notification::NOTIFY_WARNING,
+                closebutton: false,
+                titleicon: 'i/circleinfo',
+            );
+            $mform->addElement('static', 'subsectionwarning', '', $warning);
+        }
 
         $mform->addElement('editor', 'summary_editor', get_string('description'), null, $this->_customdata['editoroptions']);
         $mform->setType('summary_editor', PARAM_RAW);
diff --git a/public/lang/en/course.php b/public/lang/en/course.php
index a86319338b3..c6c32124742 100644
--- a/public/lang/en/course.php
+++ b/public/lang/en/course.php
@@ -153,6 +153,7 @@ $string['searchresults'] = 'Search results: {$a}';
 $string['sectionlink'] = 'Permalink';
 $string['showstartedcoursestask'] = 'Show courses on start date';
 $string['submitsearch'] = 'Submit search';
+$string['subsectiondescriptionwarning'] = '<strong>Subsection descriptions will be discontinued in Moodle 5.2</strong>. To add a description, use a <strong>Text and media area</strong> instead.';
 $string['supports'] = 'This activity supports';
 $string['studentsatriskincourse'] = 'Students at risk in {$a} course';
 $string['studentsatriskinfomessage'] = 'Hi {$a->userfirstname},
diff --git a/public/mod/subsection/tests/behat/subsection_actionmenu.feature b/public/mod/subsection/tests/behat/subsection_actionmenu.feature
index 867301e77ae..ef0ac99062c 100644
--- a/public/mod/subsection/tests/behat/subsection_actionmenu.feature
+++ b/public/mod/subsection/tests/behat/subsection_actionmenu.feature
@@ -103,12 +103,17 @@ Feature: The module menu replaces the delegated section menu
     And I click on "Edit" "button" in the "[data-region='header-actions-container']" "css_element"
     And I choose "Edit settings" in the open action menu
     And the field "Section name" matches value "Subsection1"
+    And I should see "Subsection descriptions will be discontinued in Moodle 5.2"
     And I click on "Cancel" "button"
     And I am on the "C1 > Section 1" "course > section" page
     # Section page. Open Subsection1 module action menu.
     And I open "Subsection1" actions menu
     And I choose "Edit settings" in the open action menu
     And the field "Section name" matches value "Subsection1"
+    # But subsection description warning is not shown in section edit form.
+    And I am on "Course 1" course homepage
+    And I edit the section "0"
+    And I should not see "Subsection descriptions will be discontinued in Moodle 5.2"
 
   @javascript
   Scenario: Permalink option in subsection action menu