"While we welcome Michael Schumacher back to Formula One, the fact is any form of in-season circuit testing is strictly prohibited, a regulation clearly laid out by the FIA and adhered to by all of the teams, " said Williams in a statement.

CNN: Motorsport: Williams block Schu testing bid

But a rule change, announced on Friday, will allow one day of testing at a non-F1 circuit if the substitute driver has not raced in F1 for two seasons.

BBC: F1 amends in-season testing rule after Schumacher row