Is it possible to get_the_post_thumbnail (Featured Image) inside a sprintf function?

I am trying to add the featured image of posts to my mega menu. I want to display the featured image inside a div tag. How would i add the featured image inside of a sprintf function?

$thumbnail = '';
    if ( has_post_thumbnail( $item->object_id ) ) {
  $thumbnail = the_post_thumbnail_url( $item->object_id );
  }


class Walker_Nav_Primary extends Walker_Nav_menu {
    
    


    function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
        if ( array_search( 'menu-item-has-children', $item->classes )&& $depth==0 ) {
            $output .= sprintf( "n<li class='topnavitem %s'><a href='%s' class="topnavtext">%s</a>n", ( array_search( 'current-menu-item', $item->classes ) || array_search( 'current-page-parent', $item->classes ) ) ? '' : '', $item->url, $item->title );
        } 
        
        elseif ( array_search( 'menu-item-has-children', $item->classes )&& $depth==1 ) {
            $output .= sprintf( "n<li class='productsnav %s'><a href='%s' class="productsnavtext">%s</a>n", ( array_search( 'current-menu-item', $item->classes ) || array_search( 'current-page-parent', $item->classes ) ) ? '' : '', $item->url, $item->title );
        } 
        
        
        
        elseif ($depth==2){
            $output .= sprintf( "n<li class='secondnavitem %s'>
            
            <div class='pictext'> \I want the featured image here
            
               <a href='%s' class="secondnavtext">%s</a>n", ( array_search( 'current-menu-item', $item->classes) ) ? '' : '', $item->url, $item->title );
        }
        
        
        
        
        else {
            $output .= sprintf( "n<li class='topnavitem %s'><a href='%s' class="topnavtext">%s</a>n", ( array_search( 'current-menu-item', $item->classes) ) ? '' : '', $item->url, $item->title );
        }
    }

    function start_lvl( &$output, $depth ) {
        $indent = str_repeat( "t", $depth );
        if ($depth == 0) {
$output .= "n$indent<ul class="nav-level-one" role="submenu">n";
}


if ($depth == 1) {
$output .= "n$indent<ul class="nav-level-two" role="subsubmenu">n";
}
        
        
        
  
    }
}

sprintf('<div>...<img src="%s" />...</div>', $thumbnail);