Both the club and the player agreed to the decision to cancel his contract by mutual agreement.
Cox joined the Reds in April 2017 on dual registration from Swanwick Pentrich Road.
He made one start and three appearances as a substitute last season.
Cox also featured during pre-season in July 2017 after signing a one-year deal with an option for a further year.
However, he moved out on loan at the start of the new campaign to gain minutes and experience and has not featured for the Reds in the 17/18 season.
Alfreton manager John McDermott (pictured) told his club`s website: “It was all about getting to know Oli, he’s a great lad and an enthusiastic player. However, he had limited chances to progress whilst he was here, so we sent him out on loan. This was for his best interest in order to get game time.
“But when you are under contract, there’s limited places you can go to get games so it was better for both the club and Oli to cancel the contract and he will be free to play wherever he can.
“I wish Oli all the best in his future career and I thank him for his attitude whilst he was with us”.