UPDATE 1-Best Buy warns on profit; U.S. unit head to leave

* Sees Q3 results significantly below a year earlier

* U.S. unit president to leave at end of fiscal year

Oct 24 (Reuters) - Retailer Best Buy Co Inc on Wednesday warned earnings and same-store sales would fall for its fiscal third quarter, and said the head of its U.S. business unit will leave as it restructures its U.S. business into physical and online units.

The company, the No. 1 U.S. electronics chain, said a number of senior managers will leave as it restructures to remove a layer of management. U.S. business president Mike Vitelli will leave at the end of the current fiscal year, and the executive vice president of U.S. operations will also leave.

The move is the first big structural change under new CEO Hubert Joly, who was brought in as the company grapples with shoppers who treat its stores like showrooms for cheaper online retailers.

At the same time, the company is waiting for its former CEO and largest shareholder, Richard Schulze, to decide whether he can put together a buyout bid.

Best Buy said it now expects earnings for the fiscal third quarter ending Nov. 3 to fall ``significantly below'' those of a year earlier, excluding one-time items, due to falling margins and declines at sales at established stores.

Analysts polled by Thomson Reuters I/B/E/S on average had expected earnings per share of 36 cents in the quarter. In the fiscal third quarter a year earlier it earned 47 cents per share on an adjusted basis.