Are you insane ??? :-) Don't sell him. Players like that are hard to come by. I have a striker in his 5th season. Managed to keep him trained to 5 stars and he has been my top scorer (and the League top scorer) for 3 of those seasons. He also scored the winner in my only CL Final win to date. He's had an indifferent start this season but he's still providing passes for goals by others and is a free kick specialist so he's going nowhere. I also have my Captain who's a 3 star DC but he gets rating of 7/8/9 every game. I'll be gutted when he retires but I'll keep him to the end because he's so consistent.
I'd say keep your guy because similar players are quite rare.