The head of Microsoft Corp's third-largest unit is to leave this summer, marking the latest high-level departure from the world's largest software company, which has seen its leadership of the technology sector fade over the past decade.

Bob Muglia, a 23-year veteran of the company, runs Microsoft's $15 billion a year Server and Tools business, which sells server software to companies.

No replacement has been named. Chief Executive Steve Ballmer said he would look for candidates inside and outside the company.

Over the last two years, for a variety of reasons, the company has lost chief software architect Ray Ozzie, office unit head Stephen Elop, entertainment and devices unit head Robbie Bach, and Chief Financial Officer Chris Liddell.

Microsoft's shares fell 1.33 percent to $28.21 on Nasdaq.

(Reporting by Bill Rigby; editing by Gunna Dickson)