When Kazuki Nakajima (right) appeared in the second Williams in Friday's opening practice session, replacing Nico Rosberg, many were wondering why.

For the last couple of races teams have concentrated on their race drivers in the Friday sessions, leaving the test and reserve driver in the cold.

When Nakajima appeared in the Williams on Friday there was immediate speculation that the move was merely a warning to Ralf Schumacher to up his game, following reports - originating on Pitpass - that the Japanese driver could replace the German at Toyota after next week's race at Indianapolis. Although Nakajima is Williams' test driver, he is a product of Toyota's young driver programme, while the Japanese manufacturer supplies Williams engines.

Speaking on Friday, Williams technical director Sam Michael explained the Japanese youngster's appearance.

"We use Kazuki for all the races where he doesn't do GP2," said the Australian, "so he doesn't have another commitment.

"He's quite useful, for a young guy," he continued. "He's consistent and you can see that in the lap times from practice as well. He's completely useable in terms of looking at tyre data and all the normal checks that you do on Friday morning and it lets him get a feel and understanding about how to go about a race weekend."

For the record, Schumacher qualified eighteenth yesterday, eight places behind his teammate. The German is one of only two drivers - the other being Williams Alex Wurz - to have been out-qualified by his teammate at every race this season.