Chris Burke provided a head-high cross from the right but the Serb appeared to hold back when he should have lunged at the ball right in front of Forest's goal.
Clark said: "The time it is a problem is when they are not in there missing chances.
"On the form he is in he would probably have expected to have scored. It was a great cross but I have no issue with people missing chances.
"Top strikers do not allow missed chances to worry them. They get back in and get on the next cross.
"He is not down as he knows I do not criticise people. That is football and he is making a massive contribution to what we are doing here at Birmingham."
Reflecting on the result, Clark added: "It was a good point. It was always going to be tough but I thought my players gave everything. They were committed and never gave in.
"Some of the football was excellent and their keeper had to make two or three great saves.
"I could not fault the players. They produced a fantastic performance. In the first half Burke and (Paul) Caddis were very impressive.
"It was probably one of our most fluent home performances and Olly Lee had a big say in this display."
- Sports & Recreation