Eircom's chief operations officer Andrew MacLeod is to leave the company at the end of September, just over 12 months after joining the company.
It is understood that he is returning to his native Britain to take up a position with Vodafone.
In a note circulated to staff recently, the company said Mr MacLeod was leaving Eircom for "personal reasons".
News of his departure took many by surprise, given that Mr MacLeod only joined Eircom in August 2006.
The 49-year-old was previously chief executive of MCI's Europe, Middle East and Africa operations, a post he assumed in June 2003.
He was also chief operating officer of Cable & Wireless Global, where he was responsible for all product, operations and infrastructure activities across Europe, North America and Asia.
Before holding that position, Mr MacLeod was strategy director and chief technology officer of C&W Communications.
He had a low profile in Eircom in spite of his title. His role included establishing the wholesale networks division within Eircom following its takeover by Australian investment group Babcock & Brown last year.
Eircom chairman Pierre Danon is believed to have been instrumental in recruiting Mr MacLeod to the business.
It is understood that he was interviewed for the role of chief executive at Eircom after Babcock & Brown assumed control from Valentia.
The job was given to Australian Rex Comb, who succeeded Phil Nolan in the role.
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