Because he/she is a manager and the job require either of people, project, planning, product or operations management, so one to succeed one should have the respective management knowledge/understanding (may not be course or bookish but actual).
I think your question is about the management study for being good manager -
If that is the case then the answer is no, knowledge is required not classroom knowledge. There are many good managers who don't have even college education but proved to be a very successful manager.
