Manchester-born 21-year-old Kiersey, who joined the Saddlers after being released by Premier League side Everton, is now out of contract as his short-term deal came to an end earlier this week.
Jack managed to make just three first-team appearances during his time with the Saddlers and although his deal has now come to an end manager Clarke insisted the door is still open for the former Toffeeman as Clarke believes that there is still plenty of potential yet to be developed.
Speaking via the club's official website, Darrell said; "Jack has been so unfortunate with injuries. There is certainly a player in there but unfortunately he hasn’t played the game minutes that I would have liked him to have played. He has had setback after setback.
"What I have said to Jack is that we aren’t a club that can be throwing money away so he is going to be working really hard on his fitness levels whilst not getting paid by us and basically when he gets his body right to what I think it needs to be for the everyday football side of things then we will have another look at him for the potential to earn another deal with us.
"What I have said to Jack is that we aren’t a club that can be throwing money away so he is going to be working really hard on his fitness levels whilst not getting paid by us and basically when he gets his body right to what I think it needs to be for the everyday football side of things then we will have another look at him for the potential to earn another deal with us.
"Unfortunately that’s the ruthless world of football. Jack is a really good lad and the door is open for him but where we are as a football club, we have to make sure we look after every penny."