The 33 year old who was released by relegated Bolton Wanderers at the end of last season, has signed a one-month deal with the Championship outfit that runs until 26 October.
Clark said: "I'd like to thank the board for allowing me to bring in Paul.
"He is an experienced defender who will enhance our playing squad."
“The injuries have left us with just two fit senior defenders,” added Clark.
"While I have been impressed with the progress of our young defenders, the injuries have left us with just two fit senior defenders.
"So the acquisition of Paul was one we needed to make.
"As a senior professional, Paul will give us that added experience which is always useful in this competitive division."