diff -u b/core/modules/media/src/MediaHandlerBase.php b/core/modules/media/src/MediaHandlerBase.php
--- b/core/modules/media/src/MediaHandlerBase.php
+++ b/core/modules/media/src/MediaHandlerBase.php
@@ -337,11 +337,17 @@
    * {@inheritdoc}
    */
   public function getSourceValue(MediaInterface $media) {
+    $source_field = $this->configuration['source_field'];
+
+    if (empty($source_field)) {
+      throw new \RuntimeException('Source field for media handler is not defined.');
+    }
+
     // Source value is stored as the main property of the source field in 99% of
     // the cases so return that. 1% can override this function and tweak the
     // logic.
     /** @var \Drupal\Core\Field\FieldItemInterface $field_item */
-    $field_item = $media->get($this->configuration['source_field'])->first();
+    $field_item = $media->get($source_field)->first();
     return $field_item->get($field_item->mainPropertyName());
   }
 
diff -u b/core/modules/media/src/Plugin/QueueWorker/ThumbnailDownloader.php b/core/modules/media/src/Plugin/QueueWorker/ThumbnailDownloader.php
--- b/core/modules/media/src/Plugin/QueueWorker/ThumbnailDownloader.php
+++ b/core/modules/media/src/Plugin/QueueWorker/ThumbnailDownloader.php
@@ -2,8 +2,11 @@
 
 namespace Drupal\media\Plugin\QueueWorker;
 
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
 use Drupal\media\Entity\Media;
 use Drupal\Core\Queue\QueueWorkerBase;
+use Drupal\media\MediaThumbnailHandlerInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
  * Download images.
@@ -14,7 +17,44 @@
  *   cron = {"time" = 60}
  * )
  */
-class ThumbnailDownloader extends QueueWorkerBase {
+class ThumbnailDownloader extends QueueWorkerBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The thumbnail handler service.
+   *
+   * @var \Drupal\media\MediaThumbnailHandlerInterface
+   */
+  protected $thumbnailHandler;
+
+  /**
+   * Constructs a new SelectionBase object.
+   *
+   * @param array $configuration
+   *   A configuration array containing information about the plugin instance.
+   * @param string $plugin_id
+   *   The plugin_id for the plugin instance.
+   * @param mixed $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\media\MediaThumbnailHandlerInterface $thumbnail_handler
+   *   The thumbnail handler service.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, MediaThumbnailHandlerInterface $thumbnail_handler) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+
+    $this->thumbnailHandler = $thumbnail_handler;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('media.thumbnail_handler')
+    );
+  }
 
   /**
    * {@inheritdoc}
@@ -22,7 +62,7 @@
   public function processItem($data) {
     /** @var \Drupal\media\MediaInterface $entity */
     if ($entity = Media::load($data['id'])) {
-      $entity->automaticallySetThumbnail();
+      $this->thumbnailHandler->setThumbnail($entity);
       $entity->save();
     }
   }
diff -u b/core/modules/media/src/SourceFieldInterface.php b/core/modules/media/src/SourceFieldInterface.php
--- b/core/modules/media/src/SourceFieldInterface.php
+++ b/core/modules/media/src/SourceFieldInterface.php
@@ -28,6 +28,9 @@
    *
    * @return \Drupal\Core\TypedData\TypedDataInterface
    *   The source value.
+   *
+   * @throws \RuntimeException
+   *   If the source field for the handler is not defined.
    */
   public function getSourceValue(MediaInterface $media);