Former Blues loanee Moritz Volz is on trial with German side Schalke 04. Volz has been without a club since leaving Town at the end of last season with his parent club Fulham subsequently releasing him in June.
Volz has joined the Schalke squad for a training camp in Jerez. The right-back was previously with Schalke before moving to Arsenal as a youngster.
Meanwhile, Sunderland boss Steve Bruce has revealed that his club can recall midfielder Jack Colback from his loan with the Blues at any point: "We have the capacity to recall Jack very quickly because he is on a youth loan and with youth loans you have the power of instant recall.
"But I've said before that the best place for him this season is learning his trade playing regularly for a Championship side.”
Colback, who scored Town’s opening goal in the FA Cup tie against Blackpool, is due to remain with the Blues until the end of the season.