Fox,who is cup tied, has been given the vacant number four shirt,after signing a three and a half yesr deal and goes into the squad to travel to Hull City tomorrow.
Said Iain Dowie to the club website: "We've been looking at Daniel for a while now, "He has continually impressed so I'm delighted to bring him to the Club "He is a player who is very comfortable on the ball, possesses decent pace and can hit a great range of passing. "He has played a lot of games for a 21-year-old and is certainly one for the future."
Fox who can play left back or centreback also spoke to the club website saying: I'm really excited to be here, as soon as I got to the Ricoh for the first time it made my mind up for me.
"I had a long chat with the gaffer and the Chairman and their ambitions to succeed and take the club forward were really impressive and match my own.
"I'm an honest player. I like to get forward and help the attack, I don't shirk any tackles and hopefully I can carry on playing as well as I was at Walsall for Coventry City."