Zigic completed his first full game of this campaign for Blues in the 2-0 win against Bristol City earlier this week.
Although he failed to get on the scoresheet at St. Andrew's, he linked up extremely well with partner Marlon King and caused the City defence all kinds of problems.
"He put a hell of a shift in," said Clark. "I’ve got the data and he was a striker that covered nearly 12 kms, which is a phenomenal amount of work.
"I think I’ve built up a type of relationship with him that he fully understands what I’m like as a manager and what I’m about and what makes me tick, and I’m the same about him. Certainly if he keeps delivering what he did on Tuesday he’s got a big part to play in what we’re doing."
Meanwhile Clark has also explained his decision to leave Keith Fahey out of recent matchday squads. The last time the midfielder played was against Millwall as a second half substitute.
"I just felt that Keith needed a bit of time out," said Clark.
"He came back from a serious injury without having any sort of minutes in the development squad. For the first part of it you get carried along because you've been out so long, it's that excitement, and then you have a bit of a lull. I've had it before, when I have come back from long-term injuries myself.
"You need some time out in terms of the games and get a bit of work into you on the training ground or with the development group, where there's not that pressure of winning. Keith played for the development squad on Wednesday and was excellent and showed a really good attitude.
"It's up to the lads who are out the team to keep performing to a high standard in training and if they do play in those development games, to put the pressure on the lads who are in the team."