author web site link, strange error

Hello guys
I have a multi-author blog site.
Every authors have personal page info, with web site and other infos

Sometimes when author insert info in Profile ex. Website, it work correctly, but sometimes it not work and when click on the link of author website i see https://www.mysitelink.con/www.authorsitelink.com and it not work…….with only few author!!!!!

i use this: <?PHP echo $user->user_url; ?>

any help??