Knox was invited back to Carrington in January for a third trial with the Old Trafford club in a bid to win over Nicky Butt and Jose Mourinho.
And the youngster revealed he was blown away by the club’s facilities.
The Scot became Livingston’s youngest ever player in 2015 when he made his first team debut – and is highly rated north of the border.
“I sat directly across from Michael Carrick during one lunchtime,” he told the Daily Record.
“It’s surreal to be sitting listening to banter between the likes of Paul Pogba and Wayne Rooney and joining all of these superstars queueing up for lunch, it was incredible.
“Jose Mourinho would be sitting next to his coaches but he’d speak a different language when he was talking to them so I didn’t understand a word.
“They were all great with me, they would take time to say hello and ask how I was doing.”
Sunderland have also been linked with a move for Knox, who has previously trained with Liverpool, but it seems the teenager’s sole focus is on continuing to impress at Livingston.