Okay, so one of your star players wants to leave due to the fact they believe they have achieved all they can at the club... however you don't want to sell him??? Well worry no longer my son, as you now have the answer...
Transfer List him (making him UN-available for loan), set squad status to not needed, offer to clubs for 100m, click continue... no club will put an offer in, and now his player status should be saying expecting to leave club & feels manager doesn't value his contribution to the club (or something along those lines), click continue until 2 days have passed, and then remove from transfer list and set squad status to Indispensable To Club / 1st Team Player (your choice), click continue to next day, go back and he should be "Happy to stay at club" at which point offer him a new contract which he will be happy to sign!
Transfer List him (making him UN-available for loan), set squad status to not needed, offer to clubs for 100m, click continue... no club will put an offer in, and now his player status should be saying expecting to leave club & feels manager doesn't value his contribution to the club (or something along those lines), click continue until 2 days have passed, and then remove from transfer list and set squad status to Indispensable To Club / 1st Team Player (your choice), click continue to next day, go back and he should be "Happy to stay at club" at which point offer him a new contract which he will be happy to sign!