Centre back Kyle Bartley has been ruled out for at least three weeks after sustaining a hamstring injury, while on-loan defensive partner Dan Burn has been recalled by Fulham.
Manchester United's Jesse Lingard has returned to Old Trafford following the end of his loan deal but Clark does hope to retain the services of Hull City striker Aaron McLean.
McLean has missed the Blues' last two outings with a hamstring strain but Clark has revealed he is already in talks with Tigers boss Steve Bruce about extending the forward's stay.
"I've been in dialogue with Steve Bruce after the New Year's Day games about Aaron, who has this little niggle," Clark told the Birmingham Mail.
However, with a defensive dilemma unfolding, Clark could be forced to sacrifice McLean in favour of paying wages for a suitable back four replacement.
"But we're in a little bit of limbo now because of the situation in terms of the centre-halves," he added.
"I need to look at that area - but it all depends on finances.
"It's a bit of a difficult position. We will just have to see what develops on one or two things."
Championship clubs are allowed five loan players in their matchday 18-man squad and with Manchester United undecided on whether they will keep Lingard for the remainder of the season, Birmingham are left hanging in the balance.
West Bromwich Albion midfielder Scott Allan remains at St Andrew's, despite not featuring since August and Clark has requested an end to the loan deal, which the parent club has refused.
Presently Blues have Bartley, Allan and Shane Ferguson (Newcastle United) on their books temporarily.
However, the defensive problem does open up opportunities for youngsters Will Packwood and Amari'i Bell, Clark said.
"They will have seen that when [young] players have come in and done well I've been prepared to stick with them," the 41-year-old said.
"Will and Amari'i are going to come into the equation and it's a great opportunity for them to respond."