The 25-year-old defender had been with the club for three weeks and featured in two reserve games for the Terriers.
But Clark told the club's official website: "We looked at Mark McChrystal but we won't be pursuing him any further.
"I know he has caught the attention of other clubs while he has been with us, but he just isn't what I'm looking for at this moment in time."
Meanwhile, Clark is monitoring the progress of Watford left-back Mat Sadler, who played in the midweek reserve team win against Grimsby.
"We are still looking at him and I am talking it over with the coaching staff. We will see where we go with that one over the next few days."