The 18-year-old American defender joined United from the New York Red Bulls' academy in January, but his signing was not announced until last month after international clearance was received.
Olosunde, 18, originally signed for United on 29 January but was subsequently forced to wait for international clearance before he could make his debut for the Under-18s last month.
The former New York Red Bulls academy product, who can play at right-back or centre-half, had been on the Red Devils’ radar for some time before completing his move across the Atlantic, and Butt is excited to see how he develops over the coming seasons.
Speaking in the latest issue of Inside United, the ex-midfielder said: "He's one that's been ongoing for a while. With the clearance it took him a while but we've got him.
"He's a good player, a nice lad and a really good athlete. Hopefully we'll see a lot of him in the coming years because he's someone we're really excited about."
Olosunde, who was a member of the USA’s 2015 Under-17 World Cup squad, was first linked with United last summer when the Daily Mail reported that he had been training with the club with the view to a permanent move.
The New Jersey native was previously set to play for Duke University after being named one of the college’s six new recruits for the upcoming 2016 season, and Blue Devils head coach John Kerr gave him a glowing review last month following confirmation of his switch to England.
"He's incredibly athletic,” Kerr told the Mirror. “He doesn't look like the strongest guy in the world, but he's pretty strong. His recovery pace is very impressive.
"He's played a number of positions. He's played centre defensive midfield, he's dabbled a bit at centre-back, but for the national team he mostly plays right back. His best position might be right full-back.
“He has so much pace that he can be like that Dani Alves type, that gets up and down the field. He loves to go forward and get to the final third.”
Olosunde obviously has a long way to go before he is ready for first-team football, but he can certainly take encouragement from the fact that fellow teenagers Marcus Rashford, Cameron Borthwick-Jackson and Timothy Fosu-Mensah have all broken into the senior setup this season.
He has also made the step up to the US Under-20s last month, and as one of the nation’s top full-back prospects, Jurgen Klinsmann is sure to be keeping close tabs on his progress going forward.