Goalkeeper David Martin has agreed a short-term deal that will see him at Millwall until January 2018.
Martin, the brother of former Lions defender Joe Martin, arrived at Calmont Road on Friday morning to train with his new team-mates.
The 31-year-old made more than 300 appearances for MK Dons before becoming a free-agent in the summer.
Martin's inclusion is expected to provide competition for Jordan Archer and Tom King.
