The academy graduate, who is now 20, did not make the grade at Old Trafford.
Shoretire has called time on his United career and has signed for Greek side PAOK this week.
"I joined Manchester United as an 11 year old boy with a dream of one day playing in the first team," Shoretire posted on social media, along with a 'thank you' graphic.
"I feel extremely proud to be able to say I have achieved that dream. To make it even more special, I was given the opportunity to represent this club in the premier league and in Europe.
"I'll forever be grateful to the many players, staff members and supporters who have played a massive part in my journey to this point.
"From the first day I arrived at the cliff training ground I have felt at home and part of the MUFC family.
It's been a tough decision for me to leave somewhere that's been all I've known for half of my life but I believe this is the right step for me.
"Once a red… Thank you @manchesterunited!"