Simple little snippet, that can easily be used in conjunction with wp_update_user()

/* Generate Unique User Nicename */
function generate_unique_user_nicename( $x ) {
	// set up args to query
	$args = array(
		'search'         => sanitize_title( $x ),
		'search_columns' => array( 'user_nicename' )
	);
	// query for user
	$user_url_exists = new WP_User_Query( $args );
	$results = $user_url_exists->get_results();
	// if user url is found, check for new one
	if( !empty( $results ) ) {
		$i = substr( sanitize_title( $x ), intval( strrpos( sanitize_title( $x ) ,'-' ) ) + 1 ); 
		if( is_numeric( $i ) ) {
			$i++;
			$y = substr($x, 0, strrpos($x,'-' ));
			$company_name = $y . '-' . $i;
		} else {
			$company_name = $x . '-1';
		}
		$new_company_name = sanitize_title( $company_name );
		return generate_unique_user_nicename( $new_company_name );
	} else {
		return sanitize_title( $x );
	}
}

/* Generate Unique User Nicename */

function generate_unique_user_nicename( $x ) {

// set up args to query

$args = array(

'search' => sanitize_title( $x ),

'search_columns' => array( 'user_nicename' )

);

// query for user

$user_url_exists = new WP_User_Query( $args );

$results = $user_url_exists->get_results();

// if user url is found, check for new one

if( !empty( $results ) ) {

$i = substr( sanitize_title( $x ), intval( strrpos( sanitize_title( $x ) ,'-' ) ) + 1 );

if( is_numeric( $i ) ) {

$i++;

$y = substr($x, 0, strrpos($x,'-' ));

$company_name = $y . '-' . $i;

} else {

$company_name = $x . '-1';

}

$new_company_name = sanitize_title( $company_name );

return generate_unique_user_nicename( $new_company_name );

} else {

return sanitize_title( $x );

}

Generate Unique User Nicenames for WordPress

Enjoy coding …

Alexander