So far there are seven candidates - six from eastern Europe - who have indicated they will be in the running.
Ms Clark, who is head of the United Nations Development Programme, holds the third most powerful position in the global organisation.
She said selecting the Secretary General was a lengthy process with hearings getting underway in a fortnight's time.
"It's all geopolitics in the end but let's hope the geopolitics is going to be informed by who is the best person for the job; what are the challenges now, what are the leadership and other skills required.
"I think that must be the central issue," she said.
It was quite a long choreography leading up to the end of the year by which time someone should be well known and able to take the reins, she said.