The keeper played seven times for United – once in the Premier League, five in the League Cup and once in the Champions League.
But after the legendary former manager retired in 2013, Amos never got a look-in under either David Moyes or Louis van Gaal.
Amos, now 30, is making his mark at Charlton – having played for ELEVEN different clubs.
And he told The Sun: “The big thing I've learned since leaving is there's a world outside Man United.
“I was going into proper men's football week in, week out. At United I had been getting a little taste of first-team football and then I'd be out.
“I'd sit and wait and wouldn't be allowed out on loan. It was difficult to get a flow of first-team games.
“So what I learned was the Saturday-Tuesday-Saturday grind of men's football."
Need a VPN? Or seeking to switch? Then support Tribal Football by clicking here to sign up with our official partners NordVPN. Not only will you receive the best VPN experience, but also great discounts by signing up via Tribal Football. Thanks for your support!