"I can understand Sanchez coming back to play a part at Old Trafford because, on his day, he is a great player," Merson wrote for Sky Sports.
"It's definitely a better United than the one he left too. They were flying before the suspension of the league. They've had some excellent performances and some brilliant results so that will benefit him too.
"He's got to come back and appreciate he's at one of the biggest clubs in the world, if not the biggest.