Depends. One of my first team players in the last 3 seasons who always got 7-8 has now dropped to 6-7-8, but strangely in the last few games he's been getting 5-6 ratings only but since I dont have important games i am still starting him. Hopefully he will pick up his form soon.

As for player with constant 5-6 ratings, you can choose to play them anyway and hope they will get better next season. This happened to one of my MC, first season always getting 5-6 regardless of how he perform (scoring goals, assist etc). But in the 2nd season he plays so much better and constantly getting 7 ratings and some 8 At the end of the day, ratings are not always important. My ST always get 8 ratings yet only scored 8 goals up to this league day ~~