A Yahoo spokeswoman declined to comment on the reasons for Morse's replacement. In a statement, Mayer called him "a trusted leader" at Yahoo who has "expertly guided" the company through some key periods and deals.

"I've personally relied on Tim's knowledge and leadership in my first few months at Yahoo. I know I speak for everyone in wishing him the best," Mayer said.

Yahoo has been on a years-long financial and technology slump, going through several executive shake-ups and rounds of layoffs.

Mayer's appointment has been generally viewed with optimism. Also on Tuesday, multiple news outlets reported that Mayer addressed Yahoo's staff and gave them details about her turnaround plan for the company. The Yahoo spokeswoman also declined to comment on those reports.

The IDG News Service