Baker & McKenzie is losing one of its top international partners to racing client McLaren.
Nigel Carrington is a member of the firm's eight-partner worldwide management committee and a former managing partner of the London office.
Corporate finance partner Carrington is moving to TAG McLaren Holdings as managing director after working with the client for 13 years.
Despite focusing on management for the past six years - managing London for four and then the firm for two - McLaren is the one client relationship he has continued.
He will leave Baker &McKenzie in October, by which time the firm will have to elect a new European member for the international management committee.
London managing partner Russell Lewin says: "Nigel was an important lawyer in building up our corporate practice in London but in the last two years on the international firm stage, he has been predominantly a manager rather than practising.
"But it's certainly a benefit to a business that, if somebody is going to leave, they are to going to do something that is still connected to the organisation that they are leaving."
As managing director, Carrington will not choose the company's outside legal advisers, but Baker & McKenzie is already its principal firm.
Last year, the firm also lost two key partners to clients. In December, banking and finance partner David Green left the firm after 12 years to join Goldman Sachs International as senior derivatives counsel.
And, in March, Graham Allen, a partner and IT specialist, left to become European managing attorney at Cisco Systems.