It was a just reward for Gomes, who scored 12 goals in 21 appearances for the club's Under-18s team this season, as he became the first player born in the 21st century to play in the Premier League.
Ex-academy chief McGuinness spent 23 years managing United's age-grade sides and believes that Gomes has the qualities required to reach the very top.
"He's a real talent," Sky Sports News quotes him as saying. "If he was Brazilian, people would be raving about him and, if he was six inches taller, people would be going mad.
"I suppose that's our country. People doubt players if they're short in stature but no-one is doubting Andres Iniesta or David Silva. He's got the potential to be that type of player and, in England, you just don't get many players like that.
"If you play him with better players, he'll get better himself and create chances for them. You don't want to build him up too soon but I'm sure they'll handle all that at United."
Gomes was one of 12 academy graduates in United's squad to face Palace on the final day of the league season, with four of them - Joel Pereira, Demetri Mitchell, Scott McTominay and Josh Harrop - being handed starts.