The England defender was informed he would be captain by boss Ole Gunnar Solskjaer if Young was to get a move away from the club.
"It's a really proud moment for myself and I'm really honoured to be captain of this great club. I've worn the armband previous but to be named captain is really special," he told Sky Sports.
"The manager pulled me to one side and told me that if Ashley leaves, I'd be appointed as the next captain.
"He wished me well and told me to keep doing what I'm doing. I was really proud, it's such an honour to play for this club, let alone captain it.
"It's fairly new because I've never actually been appointed club captain, but I've had some great captains in my time. I've learnt from some great people who do stuff well off the pitch."