The only obvious aspect here is the fact you are the one making assumptions, i can only advice you to not give credibility to every fake rumour that pops up. Alex Sandro is staying at least till summer and even if he is to go it has nothing to do with us 'forcing’ him to stay during the summer , Beppe even said if hisself with clear intentions of pointing out AS’s desire to stay... all this crap has been invented by the media, if someone is off-form and sits out of some game every now and than does not necessarily mean he wants to leave the club or holds some sort of grudge towards it.
http://www.juvefc.com/marotta-alex-sandro-wants-stay/
To answear your question regarding Ghoulam, even tho he just renewed with Napoli a couple of hours ago which makes him a even more unrealistic target(realistic maybe only by a huge transfer fee), tho i am still going to consider him as a 'realistic’ option to make my point.
List of Realistic/Approachable Left-Backs that are better or at least on the same level as Ghoulam. All the players i am about to mention are more or less on the same 'price-tag’ and availability as Ghoulam.
Juan Bernat - Bayern Munchen
Ricardo Rodriguez - Ac Milan
Filipe Luiz - Atletico Madrid
Lucas Digne - Barcelona
Fabio Coentrao - Sporting Lisbon
Jose Gaya - Valencia
Sead Kolasinak - Arsenal
Laiyin Kurzawa - PSG
Wendell - Bayern Leverkusen
Luke Shaw - Man United
Etc. etc. etc....
Than the more 'fantasy football’ options for Left-back would be:
Davide Alaba - Bayern munchen
Marcelo - Real Madrid
Cezar Azpilicueta - Chelsea
Jordy Alba - Barcelona
Benjamin Mendy - Man Citty
Raphael Guerreiro - Borussia Dortmund
Now lets be honest, there are plenty of full-backs out there if it would come to replacing him... but none come even close to a on-form Alex Sandro, especially not Ghoulam or the likes which would cost probably 10x more than what it would cost to keep Asamoah fighting for his place with Spinazzola. (I see Asamoah in current form as on same level with Ghoulam as an example)