Office Depot Inc. (ODP), the No. 2 U.S. office supply chain, on Monday said Chairman and Chief Executive Officer Bruce Nelson (search) has resigned and a search for his successor is underway.

The surprise departure came as Office Depot (search) grapples with falling market share and after fallout from a recent string of hurricanes that has hurt business in Florida.

Office Depot, based in Delray Beach, Fla., said Nelson resigned "by mutual agreement" with the board, after four years at the helm, and said it hired a recruitment firm, Heidrick & Struggles, to find a successor.

The retailer, which is losing ground to top rival Staples Inc. (SPLS), said director Neil Austrian, 64, will serve as interim chairman and CEO, while Heidrick conducts an executive search.

Austrian was formerly president of the U.S. National Football League and co-head of leveraged buyouts at investment bank Dillon, Read & Co. as well as chairman and CEO of Showtime/The Movie Channel.