diff --git a/src/plugins/discover/public/application/components/sidebar/lib/group_fields.test.ts b/src/plugins/discover/public/application/components/sidebar/lib/group_fields.test.ts
index 89980f7fd0f54a..9792e98ba84c7d 100644
--- a/src/plugins/discover/public/application/components/sidebar/lib/group_fields.test.ts
+++ b/src/plugins/discover/public/application/components/sidebar/lib/group_fields.test.ts
@@ -47,6 +47,7 @@ const fieldCounts = {
   category: 1,
   currency: 1,
   customer_birth_date: 1,
+  unknown_field: 1,
 };
 
 describe('group_fields', function () {
@@ -232,7 +233,7 @@ describe('group_fields', function () {
 
     const actual = groupFields(
       fieldsWithUnmappedField as IndexPatternField[],
-      ['customer_birth_date', 'currency', 'unknown'],
+      ['customer_birth_date', 'currency'],
       5,
       fieldCounts,
       fieldFilterState,
@@ -241,4 +242,30 @@ describe('group_fields', function () {
     );
     expect(actual.unpopular).toEqual([]);
   });
+
+  it('includes unmapped fields when reading from source', function () {
+    const fieldFilterState = getDefaultFieldFilter();
+    const fieldsWithUnmappedField = [...fields];
+    fieldsWithUnmappedField.push({
+      name: 'unknown_field',
+      type: 'unknown',
+      esTypes: ['unknown'],
+      count: 0,
+      scripted: false,
+      searchable: false,
+      aggregatable: false,
+      readFromDocValues: false,
+    });
+
+    const actual = groupFields(
+      fieldsWithUnmappedField as IndexPatternField[],
+      ['customer_birth_date', 'currency'],
+      5,
+      fieldCounts,
+      fieldFilterState,
+      false,
+      undefined
+    );
+    expect(actual.unpopular.map((field) => field.name)).toEqual(['unknown_field']);
+  });
 });
diff --git a/src/plugins/discover/public/application/components/sidebar/lib/group_fields.tsx b/src/plugins/discover/public/application/components/sidebar/lib/group_fields.tsx
index c7242a8518b553..eefb96b78aac66 100644
--- a/src/plugins/discover/public/application/components/sidebar/lib/group_fields.tsx
+++ b/src/plugins/discover/public/application/components/sidebar/lib/group_fields.tsx
@@ -64,7 +64,9 @@ export function groupFields(
     } else if (field.type !== '_source') {
       // do not show unmapped fields unless explicitly specified
       // do not add subfields to this list
-      if ((field.type !== 'unknown' || showUnmappedFields) && !isSubfield) {
+      if (useNewFieldsApi && (field.type !== 'unknown' || showUnmappedFields) && !isSubfield) {
+        result.unpopular.push(field);
+      } else if (!useNewFieldsApi) {
         result.unpopular.push(field);
       }
     }