Amass has spoken of his delight at getting the deal over the line.
The 18-year-old told swfc.co.uk: “I’m very excited, I can’t wait to get going and I’m just really happy that it has all happened.
“I think as a player, I would say I’m exciting, I’m confident, I’m hard-working and really ready for this challenge.
“One of my biggest strengths is that I believe in myself, I know what I’m capable of and my main goal is to perform week in, week out and show consistency.
“I want to be exciting for the fans to watch.”
Amass also said: “I just had a good feeling instantly when I spoke to the manager.
“I got the feeling that this will be the best place for me, the history of the place is massive and that’s why I chose here.
“I think I’ve learned a lot, the move to Manchester United was a good step, the right step for me and since then I’ve been with the first team.
“From that I have taken a lot of things, learned a lot of things and it has really developed me as a player.”