Tesco said its recently appointed UK and Ireland boss Charles Wilson would step down to a less onerous role after being diagnosed with throat cancer three months ago.
Wilson, the former CEO of wholesaler Booker which was bought by Tesco in March, had been seen as a potential heir to Tesco chief executive Dave Lewis.
He had been appointed to run Tesco's largest division only five months ago.
Tesco veteran Jason Tarry now becomes CEO of the UK and Republic of Ireland business, reporting to Lewis.
His previous role as group chief product officer was handed to Andrew Yaxley, the boss of the Ireland unit.
Wilson, 52, has been responding well to radiotherapy and the signs were that the treatment has been successful, Tesco said in its statement today.
He was diagnosed with cancer after an operation to take out his tonsils.
To help ease his workload, Wilson will focus on leading the Booker business and delivering the cost synergies and growth plans from the combination with Tesco.
Wilson will continue to report to Lewis.
The reshuffle of Tesco's top management team comes at a time of change in Britain's supermarket sector as Tesco faces losing its long-held number one spot in the UK to second-ranked Sainsbury's which agreed to buy Wal-Mart owned Asda, the number three player in April.
Tesco said the management changes would be effective from July 16.
The moves also come after Tesco announced it will form a "strategic alliance" with French retailer Carrefour as part of efforts to cut prices.
The long-term deal will be covered by a three-year framework and see the two companies form a "strategic relationship" when dealing with global suppliers.
In June, Tesco reported its 10th consecutive quarter of sales growth, boosted by its acquisition of Booker.
Tesco's UK supermarket sales rose 2.1% on a like-for-like basis, while Booker's sales, including tobacco, jumped 14.3% over the period.
