Heidfeld could return to Williams in 2010
The German veteran, 32, drove for the then BMW-powered team alongside Mark Webber, before moving with the Munich manufacturer to its new works team.
Other drivers linked with Williams for 2010 are Heikki Kovalainen, Rubens Barrichello and Timo Glock, with the Grove based team expected to part not only with the Brawn-bound Nico Rosberg but also his Toyota-backed teammate Kazuki Nakajima.
Technical director Sam Michael admits he still rates Heidfeld highly.
"Against Kubica, Nick looks very good. To say that his career is over would be ridiculous," the Australian is quoted as saying by Auto Bild Motorsport.
It is believed that Williams is looking for an experienced driver to be German rookie Nico Hulkenberg's 2010 teammate.
"Today there are many advantages to having experienced drivers, because as everyone knows there is no testing. Taking on a rookie is a risk, without a doubt," Michael added.
If the FIA gives a green light to a fourth team being powered by Mercedes next year, Williams is in 2010 expected to take over the Renault engine supply currently used by Red Bull.
Said Sam Michael: "We are still in the middle of that decision."