Clarke has missed City's last five league games after picking up a troublesome calf problem.
Given Clarke's undoubted ability, McCall would understandably like to be able to call upon the Irishman's services as soon as possible but the City chief knows that he can only come back when everything is completely right.
McCall said: "Unfortunately calf injuries can be slow ones to heal properly.
"We cannot rush him back to feature in one game and then risk him getting injured again.
"We still have the whole of the second half of the season to come and we want Billy available, at least for the vast majority of that anyway.
"If that means waiting an extra week or so, then so be it.
"I can speak from personal experience myself, coming back too soon from calf injuries can put you out for longer.
"It is a slow process but we did have a scan on his injury the middle of last week and it did at least show his tear had reduced greatly.
"He has stepped up his recovery work but you still have to be patient to see if he feels anything again.
"We will just have to bide our time at the moment and see how Billy progresses."