Defender Jack Smith has signed a short-term deal with The Lions that will keep him at the club until next January.
The former Swindon Town player has been training with the club since the beginning of pre-season and travelled to the Republic of Ireland with the squad last month.
"My first goal is to push into the team and take it from there," Smith told the club's official site on signing. "I'm really looking forward to my time here. It's down to me to force my way into the team, play well and hopefully earn myself a longer contract."