How to use regex for when link contains a specific string?

Question

How to create a regular expression for when a link contains wp-content/uploads path? The problem is somewhere in this wp-content/uploads part.

You can see an example here https://regexr.com/3ro5n

(<a.*? href=".+?(?:\/wp-content\/uploads)+")><img

In the end I am trying to add a class to this links for Lightbox, if those links contain an image

function give_linked_images_class($content) {

  $classes = 'fancybox';

  if ( preg_match('/<a.*?><img/', $content) ) {
    $content = preg_replace('/(<a.*? href=".+?(?:\/wp-content\/uploads)+")><img/', '$1 class="' . $classes . '" ><img', $content);
  }
  return $content;
}

add_filter('the_content','give_linked_images_class');