Sell or Allow To Retire/Move On

I have a player (DR, DC) whose contract will expire at the end of this year. He isn't a poor player, but he also does not start. I play with 4 defenders, and have 2 substitutues. He is the "odd man out" so-to-speak, and is essentially a reserve player for injuries. When I purchase another defender next season, he would be bumped even further down the list or, more likely, would be sold.

If his contract is set to expire at the end of this year, I assume it would be better to sell him now than to simply let his contract run out and not receive anything for him, correct?

Or would it be better to renew his contract and sell him early next season?

If this is last season, then you can't extend his contract or sell him.
If this is not his last season, sell him, save money! :)

you get 7 days to renew a players contract that expired at the end of the season, so dont be worried if he doesnt sell this season

It is better to sell him this season, otherwise for renew is contract next season you have to pay the fee, and His value Will be lower, so you lose in 2 ways.