It gave Rangnick the opportunity to make 11 changes for his second match as interim boss, with United’s homegrown forward shining brightest and scoring an outstanding acrobatic volleyed opener in a forgettable 1-1 draw.
“I think today he also showed not only the quality because of that beautiful goal, but also the way that he set up the opportunity for Juan Mata was brilliant,” the German said.
“He’s a massive talent – left foot, right foot, good on the ball. Also the way that he set up the goal for Fred on Sunday, so it’s about continuity.
“He has to develop physically but technically for his age he is a great player.
“My job is to develop him, to make an athlete out of him and if he manages to do that, he can be become a regular player for this club.”
Rangnick knows a thing or two about the world’s best young attackers, having helped bring Erling Haaland to RB Salzburg – one of United’s potential last-16 opponents – when working for Red Bull as head of sport and development.
“They are a different kind of striker,” he said when asked how the Norway striker compared to Greenwood in terms of ability.
“Erling, for me, is a target striker, who can play as a single striker like a target man or together with another striker in a 4-4-2.
“I think Mason is more of a nine-and-a-half. He can play as a striker, he can also come from the wing, he can play together with another striker and he’s very technical. Left foot, right foot.
“And as I said, sometimes he looks a bit not on an athletic level. I think we have to develop him there physically, but technically all the things that he can do with the ball are outstanding.
“So, I am not so much worried about his technical level. We need to develop him physically and mentally to become the strongest version of himself.
“And if we manage to do that, he can become a regular player and a valuable player for our club in the future.”
United were unable to build on Greenwood’s fine volley, with 19-year-old Fabian Rieder scoring an outstanding equaliser as Young Boys capitalised on poor sloppy play.
Donny Van De Beek and Aaron Wan-Bissaka were involved, with the latter ending the night receiving treatment by the advertising hoardings.
“He received two knocks – one again unfortunately on the wrist and the other one on his knee,” Rangnick said of the right-back, who has been out with a wrist issue.
“He’s been treated now in the locker room but we have to wait and see what the situation around those two knocks will be like tomorrow.
“But I am positive that he can the day after tomorrow train again and hopefully become part of the team against Norwich (on Saturday).”
The draw ended Young Boys’ European campaign, with former Huddersfield boss David Wagner frustrated they did not take more from Wednesday’s trip to Old Trafford.
“We know where we’ve come from,” he said. “We’re the Swiss champions.
“It was a difficult group and we’ve picked up five points – the most Young Boys have ever won in a group stage.
“We had chances in the second half to get the result we needed, but it wasn’t to be. On another day it could have been different.”