if u sack him it wont cost you its his season wage also when you don't have 14 players for new season game generate retired players to cover the shortage
I understand that you will feel bad if you need to pay to sack him. But on another side, I guess that you have not paid any token or sign-on fee to sign him.
I heard that many teams at high levels seriously lack cash to sign players. As experienced manager, I believe you should fully understand this even if your team may be an exception and rich.
You must normally in the habit of resigning contracts before the season starts because otherwise you'd have seen that the system adds these players to any team that doesn't have 14 signed players.
Why Do I Get Unknown Players? - Top Eleven be a Football Manager #explained
You don't need to pay money to sack him if you didn't buy him. I've got few players like that last season because I had a lot of players whose contract expired. Then I sacked those retiring players for free and signed new contracts with mine players.
Ex top eleven player