JACKSONVILLE, Fla. (AP) — Shares of CSX slid Friday after the railroad said CEO Hunter Harrison will take a medical leave "due to unexpected complications from a recent illness."

Chief Operating Officer James Foote will serve as acting CEO of the Jacksonville, Florida, company.

Harrison, who has engineered turnarounds at three different railroads, was hired in March after activist investors pressured CSX for changes. But questions have emerged about his health. In May The Wall Street Journal reported that Harrison often works from home and occasionally uses oxygen because of an undisclosed health issue. Harrison then told the newspaper that doctors had cleared him to work.

Shares of CSX Corp., which has operations in Nashville, fell $4.38, or7.6 percent, to close at $52.93 Friday. Shares hit an all-time high this week and are up 47 percent in the year to date.