Michael Patrizio has been chief executive of Qatari Diar's UK arm since June 2013, but will leave next week to return to the US "due to ongoing family concerns", according to property industry magazine Estates Gazette.
He joined the company, which has stakes in The Shard and the former Athletes' Village at the Queen Elizabeth Olympic Park, five years ago.
The company is a subsidiary of the Qatari Investment Authority, which is currently in a takeover battle with Canary Wharf owner Songbird Estates. Although the Songbird board has advised shareholders against accepting the Qataris' 350p-a-share offer, it has yet to be rejected outright.
Sheikh Jassim bin Hamad Al Thani, Qatari Diar's regional director for Europe and its UK chairman, will take on chief executive duties at Qatari Diar on an interim basis. He paid tribute to Patrizio, saying the team had "achieved significant milestones over the past 18 months".