The criteria here are way too strict. Touted at a young age but done absolutely nothing? There's barely anyone who fits that description.
Lifting the OP's restrictions a bit, just from United you could have:
Federico Macheda - Burst onto the scene in the most dramatic fashion possible, and was soon touted as a future world class striker. Failed to get close to that immediate hype.
Ravel Morrison - By all accounts had the talent to be one of, if not the best player in the world. Attitude and personal issues seriously set him back and now he's just another "what if?"
Adnan Januzaj - Had a much more prolonged introduction than Macheda, but the hype was very much sky high. Doing alright for himself, but certainly never lived up to the billing that saw him earn the 11 shirt.
Phil Jones - A monster for football. The next Duncan Edwards. Apparently just asked to not have a testimonial because no one would turn up. Perhaps most famous for pulling odd faces.
Fabio da Silva - Rafael broke through first, but all of the talk was how his twin was the better player. He wasn't.
Paddy McNair - I think van Gaal said he'd be our right back for the next ten years. At Middlesbrough.
Outside of United:
Anthony Le Tallec - That article.
Mark Gonzalez - Liverpool went to great lengths to sign this guy, only to ship him out after a single season.
Jon Flanagan - Just been released by Rangers.
Gael Kakuta - Cost Chelsea a fair bit of money in settlements. Not sure he ever played for them.
Jon Obi Mikel - Signed for us. Didn't sign for us. Chelsea paid us for him. He was sort of alright.
Bojan Krkic - He was the next Messi, until he ended up at Stoke. Miraculously made over 100 appearances for Barca.
Adam Llajic - So good we signed Zoran Tosic just to keep him company. Ended up not signing for us so we kept Tosic around seemingly to offer high first goalscoring odds at the in stadium bookies. Llajic hasn't had the worst of careers though.
Micah Richards - IIRC he very briefly had the right back spot locked down for England. Remember watching him chasing someone back for City and just giving up. About sums up his career.
Carlos Vela - Somehow stayed with Arsenal for 7 years. Now Zlatan's MLS nemesis.
Joaquin - The next big thing in Spanish football. Last capped before Spain got good.
Lassana Diarra - Chelsea, Arsenal, Real Madrid. Did nothing at all of them. Inexplicably was at PSG last year.
Igor Akinfeev - Future world's best GK. Never left CSKA.
Jack Butland - England's number one for years to come. Currently still playing for Stoke, albeit near the bottom of the Championship.