However, the 25-year-old defender has recently undergone an operation on a hip injury and so any deal has been put on hold until the new transfer window opens in January.
"We agreed a deal for Zak with Millwall, but because he has just had a hip operation, the player felt it was better if he remained at the club until he was fully fit again." Jenkins told the club's official website.
"We will review the situation again in January."