CSX CEO Hunter Harrison has passed away at age 73, the freight rail company confirmed in a statement Saturday.

"It is with great sadness that we announce that E. Hunter Harrison, President and Chief Executive Officer of CSX, died today in Wellington, Fla., due to unexpectedly severe complications from a recent illness," the company said.

Harrison had taken medical leave on Thursday, sending shares of the third largest U.S. rail company tumbling in pre-market trading. Jim Foote was named acting CEO in his place.

Harrison had been suffering from an undisclosed medical condition that forced him to work from home some days and use an oxygen machine at times, according to the Wall Street Journal.

"With the passing of Hunter Harrison, CSX has suffered a major loss," board chairman Edward Kelly said.

"Notwithstanding that loss, the board is confident that Jim Foote, as acting chief executive officer, and the rest of the CSX team will capitalize on the changes that Hunter has made."

CSX is in the midst of a controversial effort to boost profits by streamlining its operations, which has drawn customer and regulatory scrutiny.

Harrison served as CSX's CEO for less than year. He was brought on board in March to lead a turnaround program at CSX, after earning a reputation as a tough cost-cutter as the head of Canadian Pacific Railway.

"The board will continue to consider in a deliberative way how best to maximize CSX's performance over the long term," Kelly said.

Reuters contributed to this report

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