Mark Smith has left his position as technical director of Sauber only nine months after being appointed.
A statement from the Swiss team said Englishman Smith, 54, had "decided to go back to the UK for family reasons. He has already left the company".
Smith, previously technical director of Caterham, Force India, Jordan and Red Bull, was appointed on 1 July, 2015.
The move leaves Sauber without a technical director before the start of the new season in Australia this week.