Lee is without midfielders David Livermore and Jody Morris through suspension while Andy Marshall, Matt Lawrence, Mark Phillips, Jamie Vincent and Ady Williams are injured.
"It was imperative that we brought in a centre half," Lee told the club's official website. "And in that respect I am pleased to have signed Zak from Liverpool. I'd also like to welcome Colin from Birmingham. With Marsh's injury, the end of Paul Jones' loan period, plus Terry Masterson deciding to take a break from football and returning to Ireland, we needed a keeper.
However Colin can't play on Tuesday, so that is a situation that we will have addressed in time for that game."