Sancho, 20, has been strongly linked with a move to Old Trafford this summer, although Dortmund have insisted he will not be sold.
The England international has developed into one of the most exciting players in Europe since leaving Manchester City in 2017, scoring 34 goals in 99 games for Bundesliga club Dortmund.
Fletcher says Sancho’s development has been ‘fantastic’ and has backed his former club Manchester United to secure his signature this summer.
‘At his young age, to be doing what he’s doing at that level of football is fantastic and there’s no doubt that he has got a bright future in the game,’ said Fletcher, who won five Premier League titles and the Champions League at Old Trafford.
‘It’s clearly a position that Manchester United, I feel, have needed for a number of years now, somebody who naturally wants to play off that right-hand side.
‘So, I think that it ticks all the boxes in that respect but – at the same time – these transfers are very, very difficult.
‘Large sums of money in these times, there’s a lot of circumstances involved in it.
‘It’s not just Jadon Sancho and his representatives, it’s Borussia Dortmund, it’s Manchester United and I’m sure there will be other clubs interested in him as well.
‘He’d be a fantastic acquisition for anyone who gets him.’
Another former Manchester United title-winner, Wes Brown, also wants to see Sancho arrive through the doors at the Theatre of Dreams.
He said last week: ‘We’ve got some young, exciting attacking players but Sancho would be another layer of the cake.
‘He’s exciting, he’s young, he can score goals and is good with assists. If they can get that done it would be perfect.
‘United can always improve. The defence, midfield; the more competition going on all over the field, the better the team becomes.’
Manchester United begin the 2020-21 Premier League campaign with a trip to Burnley.