TOM King is set to move on loan to Forest Green Rovers.
King, 22, has made just two appearances this season, both in the EFL Cup.
He has been kept out of the match-day squad by David Martin, who signed a short-term deal in September before extending it until the summer.
King made his senior debut last season, and went on to keep six clean sheets in 17 games in 2016-17.
Forest Green are 22nd in their first-ever campaign in League Two.
Meanwhile, James Brown will have his loan deal with Carlisle extended until the end of the season.
Image: Millwall FC