Midfielder Eugen Bopp has joined the Blues on a week's trial. The 22-year-old was released by Nottingham Forest at the end of last season.
Boss Jim Magilton told the club site: "Eugen will spend the week with us and we'll see how he gets on.
"It will give us time to look at him and him time to look at us."
Former Celtic, Sunderland and Livingston midfielder Colin Healy is already training with the Blues, looking to win himself a full-time contract. Healy has been pencilled in to play 45 minutes in the first pre-season friendly at Boston next Saturday.
Bopp joined Forest in August 2001 after spending time with Bayern Munich as a youngster. Although born in Kiev in Ukraine, Bopp is German and has represented them at U21 international level. Should he sign, Bopp would become the club's first ever German player.
In his five years at the City Ground Bopp made 89 appearances and scored 11 goals.