Shmoo on "Trying to remove with and height attributes off get_avatar"

Just curious why does my filter not work?

// Remove height/width attributes on avatar img tags.
function myscript_remove_dimensions_avatars( $avatar ) {

    $avatar = preg_replace( '/(width|height)=\"\d*\"\s/', "", $avatar );

    return $avatar;

}
add_filter( 'get_avatar', 'myscript_remove_dimensions_avatars', 10 );