Reports in Spain this week have strongly suggested Ronaldo will seek to leave Real in the summer with relations with Florentino Perez at an all-time low.
The Real president is said to be willing to let Ronaldo leave in order to form a new, young front three to rival that of Barcelona.
Harry Kane, Neymar, Mauro Icardi and Eden Hazard have all been touted as potential targets for Los Blancos.
And United are supposedly willing to take advantage of Ronaldo’s current situation by bringing him back to Old Trafford, nine years after leaving the club.
However, Arsenal legend Merson believes it wouldn’t be a smart move for the 32-year-old.
“We’ve got a very good lasting memory of Cristiano Ronaldo in the Premier League,” Merson told Sky Sports’ The Debate show.
“I wouldn’t like to see it.
“You’re talking about one of the best players.
“I got a lasting memory of him as an unbelievable player.
“I wouldn’t like him to come back here and struggle and he could.”