Crewe Alexandra defender Toby Mullarkey has joined Blues on a one-month loan deal.
He will be joining his team-mate Andre Brown at Harrison Park after he completed a similar move earlier in the week.
Mullarkey helped the club's Youth team reach the quarter-final stage of the FA Youth Cup before they were beaten by a very impressive Manchester City side, having knocked out Arsenal in the previous round.
Casswell has also signed Tyler Williams from Goole and Warren Burrell from Sheffield in a week of hectic transfer activity at the club.