Some players just don't play well at first, I have quite a few on my team 2 scout midfielders I brought one last season one this season, the guy from last season averaged 5s towards the end he averages 8/9s and has done this season aswell, the other guy is my only 7* and has been getting as low as 4's he got 7 in his last game so I think his form is picking up, but unfortunately you cant really tell when they change^
I also have a few beast players one who I actually named messi my Amc top scorer 2 seasons in a row no one came close:P

I also have trouble with one of my strikers so recently have only put 1 striker on and hes a scout but doesn't score enough, the other one is a 4 star youngster who had average games and barely scored recently tried him again and he went on to score 4 goals and 3 assists +mom

So I think it can be quite random switching there postion might work for e.g. rotating the striker to be in the middle or switch sides with the other striker, change his arrows.
Not much you can do as it is pretty much luck of the draw^