The garage fire that overshadowed Williams' first win in Formula One for seven and a half years on Sunday, after Pastor Maldonado had taken the chequered flag, caused severe damage.
A considerable amount of equipment was destroyed in the blaze, leaving Williams little time to replace or repair ahead of first practice in Monaco next Thursday.
The links between the two teams are significant as three former Williams engineers are now employed by McLaren, while Jenson Button started his F1 career at Grove.
Sporting director Sam Michael, technical director Paddy Lowe and director of development/design Neil Oatley, offered help immediately the ashes settled on the incident in Barcelona
Williams, however, still face difficulties as described by their chief operations engineer Mark Gillan, who said: "We lost a lot of equipment, including IT equipment. We will have everything we need to run operationally at Monaco, but we may be missing a few of the extras."