The full-back damaged his ankle ligaments after tripping in the gym last week and the diagnosis is worse than first feared.
"We've lost Mitch Hancox for a minimum of six weeks," confirmed the Blues boss.
"On Saturday the season only has eight weeks left so it will be extremely doubtful we’ll see Mitchell again (this season). It could potentially be even longer if he needs an operation. When he’s in the team, more times than not we get a positive result, so it's a blow."
Clark also has a number of other concerns heading into Saturday’s big game against QPR.
"Lee Novak has got a bit of a tight hamstring, so we’re monitoring that," he said.
"We're testing Albert Rusnak as well, because he’s missed the last few games with a tight groin. Brian Howard picked up an ankle injury on Tuesday against Hednesford so he won’t be available.
"Fingers crossed that my internationals come back unscathed, because we’re running out of numbers again."
The latest casualties join Matt Green (knee), Akwasi Asante (hamstring) and Neal Eardley (knee) on the sidelines.