The 18-year-old has represented United from under-10s level through to the development squad and is one of the first beneficiaries of new owner Massimo Cellino's youth policy.
Sam Byram and Alex Mowatt have made the step up to the first team in recent seasons and more promotions are likely under the leadership of Cellino.
"I was very surprised to get the call," Skelton told the club's official website.
"But I went back into training last Thursday and Neil Redfearn told me that I was training with the first team. I was a bit surprised as it came out of nowhere.
"In these two weeks away I'm just going to try and be myself. I was nervous when I was first told but I think that nerves are good to be honest.
"It shows that you're ready for it. It shows that you are ready to give your all, and that's what I'm going to do.
"I can relate to Alex and Sam who have been in my shoes before so that gives me inspiration to take this opportunity with both hands.
"I'll just try my best and give it my all if given the chance."
Meanwhile, Jamaica international Rudy Austin has joined the squad in Italy ahead of friendlies against FC Gherdeina on July 10 and FC Viitorul Constanta three days later.