It was confirmed yesterday that McTominay had chosen Scotland over England.
"It's a great coup for Scotland," said former Manchester United midfielder Fletcher yesterday.
"This is somebody who is playing in the Premier League and the Champions League.
"He's really forced his way into the Manchester United team in the last few weeks and is someone who is going to have a bright future in the game to play for us.
"I'm sure England were desperate for him, as well, with the World Cup coming up this summer.
"You want form players. Central midfield probably isn't their strongest position, so I'm sure if he stayed in the United team that would have been an option for them. But he has a desire to play for Scotland, so that's great."