Williams is holding Nico Rosberg and Kazuki Nakajima to their contracts until the last day in December.
It is believed the decision explains the hold-up in an announcement about Rosberg's team for 2010, with the German's deal not likely to be made public until after 1 January.
"Nico Rosberg and Kazuki Nakajima remain our drivers until the end of 2009," reads an excerpt of the media statement in which Rubens Barrichello and Nico Hulkenberg were confirmed as Williams' drivers for next season.
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