As long as the keeper is doing well, I'd keep him.
The ratings imho is deduced from whether he made any saves in a normal situation.
Just won another team 11-0, my keeper's not moving much (opponent only 5 Shots on target), so only received a 5 rating.
In other matches (I recall), if he made 3-4 saves, he easily gets a 7-8.
I believe if one were to set their keeper to take Free Kicks, Corners and Penalties, he could have a higher rating as well