Ratcliffe says if Baines follows David Moyes to Old Trafford, it would leave a much bigger gap than if Fellaini exited Merseyside.
"Marouane Fellaini could also leave but Baines is the main concern," Ratcliffe told talkSPORT. "If he wasn't scoring he was creating goals, I think he created more than any other left-back in the Premier League last year, certainly more than Ashley Cole.
"His free kicks and set pieces in and around the box are quality, and he's improved massively as a defender as well.
"He's a proven international now, he's battling it out with Cole for the number one left-back spot for England, so he'll be a big miss."