The 17 year-old is away with Argentina this week.
Garnacho paid tribute to several key influences in his career to date, including coaches and senior figures at United who have helped him.
“My whole family have supported me in every kind of decision that I've taken, and my agent Carlos is just like family to me," he told manutd.com.
“Within the club itself, I'd also like to thank all the staff and all my team-mates who have constantly been helping me to improve. My Under-18s coach, Travis [Binnion], who I started to work with eight months ago, has helped me a lot and I've come on so much as a footballer thanks to him.
"And now in the Under-23s with Neil Wood and Neil Ryan, who are two great coaches who are always helping me and want the best for me. I'd also like to thank Justin [Cochrane] and Darren Fletcher who are two other people within the club who have always looked out for me, giving me their support in all kinds of decisions."
And he revealed Mascherano, also formerly of Barcelona, has had key input.
"Away from the club, I'm very grateful to Javier Mascherano, the Argentina Under-20 coach. Since they were first interested in me two or three months ago, he has always paid close attention to me, looking out for me and being attentive and thoughtful."