When Nike said on Thursday that John Donahoe was stepping down as chief executive officer, his exit from a rocky tenure offered a brutal reminder to corporate boards: Focus on what a company's core business is when looking for a new CEO.

The shoe giant's shares are down over 20% year-to-date after an ambitious direct-selling strategy opened the door to competition.

After losing market share in recent years, Nike faces near-term challenges such as the sales momentum among competitors.