Powell, a summer signing from Crewe, was handed his first United start in Turkey on Tuesday and came closest to scoring with a header that crashed against the crossbar.
The appearance against Galatasaray turned the 18-year-old into the second youngest Englishman ever to play for the Red Devils in Europe's most prestigious competition.
To underline how rapidly Powell has risen, just a year and a day previously he was appearing in front of barely 2,000 spectators in a League Two match at Morecambe.
It may seems like a completely different world but Fletcher feels it could prove to be a very useful asset.
"Playing in the lower leagues as a teenage will have hardened him up," said Fletcher.
"In some ways it is a better grounding because you get toughened up.
"You play with and against good experienced pros in the lower leagues, players who are going to kick you. You have to learn how to survive.
"It may not be the grounding in terms of what you expect of a Manchester United player but you are playing in games that matter so mentally and physically it is hard."
Fletcher cannot speak from personal experience because the Scot has spent his entire career at United.
What he does know is just how much Powell will have gained from the environment he found himself in on Tuesday.
Fletcher was 20 when he was part of the United squad beaten by Fenerbahce in 2004.
It proved a costly loss as it pitched the Red Devils into a knockout round meeting with AC Milan, and from that, immediate elimination.
Nothing quite so drastic will happen as a result of last night's loss at the Turk Telecom Arena, which merely heightens the benefits Powell will have gained.
"You realise in matches like these how quick the game is and that your touch has to be right," said Fletcher.
"I came to Istanbul as a 20-year-old to play Fenerbahce and it was a real eye-opener.
"I didn't expect the ferociousness of the crowd. Playing in that atmosphere then was a real shock to the system.
"I now know what to expect and have been fortunate to play in a lot of big games in Europe and big atmospheres but that one certainly helped."
Powell has not been at Old Trafford very long, and his first-team exposure still only extends to four games.
However, he has been around long enough to give the impression he will soak up the information, with Sir Alex Ferguson confident enough to talk of the youngster as a potential successor to Paul Scholes.
Fletcher does not want to burden Powell with such comparisons, and feels he would be better served by concentrating on making the most from his talents.
"Nick is coming on leaps and bounds," said Fletcher.
"When a player comes from Crewe you don't really know what to expect but his touch, awareness, ability and eye for a goal is great.
"Physically he is powerful already but he can get even stronger.
"I am not saying he is another Scholesy because he is the best player I have ever played with.
"Let's just hope can concentrate on being Nick Powell because I am sure he will be a great player for Manchester United."