First of all we are talking youth players. Young trainees who were well thought of, had a reputation in the footballing world at a young age and were getting people talking. There were probably 10-12 players who I thought were fabulous to watch, exciting, scored goals, dynamic, different, x-factor type players. 4-5 I just knew (with luck, no injuries etc) were dead certs. They were:
Norman Whiteside, Ryan Giggs, Nicky Butt, Wes Brown and Mason Greenwood.
Others were almost dead certs but I thought they lacked something. This is purely personal opinion and others may have seen things differently. I often changed my mind about them from week to week.
Mark Hughes - physical with a magic first touch, he seemed slower and would often be inconsistent for long periods
Paul Scholes - he was very small at first, got bullied a little, had asthma problems. He wasn't part of the 1992 team because of that.
Darren Fletcher - technically brilliant, extraordinary passing game but lacked pace
Guiseppe Rossi - quick, natural goalscorer but seemed one footed and often marked out of games by bigger players
Danny Welbeck - quick, direct, physical but he was like bambi on ice at times and would sulk
Ravel Morrison - had it all in bucketloads but his emotional intelligence off the pitch was always going to be an issue (probably the most naturally talented player I've ever seen at that level).
I am probably missing a player or two here.
The other things that can help/hinder your viewpoint is how strong the others in the team are. If you play in a good team, that can help you as your flaws are covered up by other players but you don't stand out as there are other good players too. Other prospects can look brilliant but that's because they are stand-outs in an average team. Your viewpoint is influenced by making comparisons. The players listed above were all 'standouts' in good/very good teams. A lot of them made their first team debuts early too.
Then there were others where I believed had a chance but certain facets of their game might hold them back so I was never too sure. Players in this category were P. Neville, Pogba, Evans, Pique, Gomes, O'Kane, Curtis, Lingard. Some still had good/great careers but I always had doubts as far as United were concerned. David Beckham is an interesting example in this group. Up until 19/20 he wasn't that special but was a late developer. So as a youth player not really on my radar.
Ones who made it, but I didn't think they would, were the likes of Clayton Blackmore, Lee Martin, Gary Neville, John O'Shea, Marcus Rashford, Scott McTominay. I guess the defensive players don't stand out as much in terms of flair, skill etc. Scott was extremely left-field as he was so small at 15-18. I never saw him coming through and it's a testimony to his professionalism and attitude that he's had such a good career. Marcus was the same. He was the type of player who made the difficult transition from reserves to first team look easy. Sometimes you don't know unless you give them a chance.
There have also been plenty of players who I thought would go on to have good careers and they didn't. That has taught me to wait and see before making predictions. Gabriel looks the real deal but I don't think I see him as a 'dead cert'...at least not yet.
But those top five players were obvious to me from the start.