The Portuguese winger is rumoured to be close to joining the Serie A giants after a thoroughly disappointing few seasons at Old Trafford.
However, van Gaal is keen to keep the skilful wide-man ahead of his potential arrival.
The Dutchman is thought to be ready to implement a system at Old Trafford that will feature wingers, and is not ready to let his options be reduced before he arrives.
Nani only signed a new contract at United last summer, yet a £10m move to Juve has been edging closer in recent days amid talk that he had no future at the Theatre of Dreams.
The man once compared to Cristiano Ronaldo may well be willing to stay put, with United set to undergo a serious change in the coming months on the back of a disastrous year.
Van Gaal has not yet been named as the current Premier League champions’ manager, however his presence for next season is expected to be made official in the coming days.