Powell, a summer signing from Crewe, was handed his first United start in Turkey on Tuesday night 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.
"Playing in the lower leagues as a teenager 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."
He went on: "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 night. 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 Tuesday 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."