"I'm delighted to see that a team like Mercedes lists Valtteri as a potential replacement for Nico," Williams said.
"We have always known Valtteri is one of the sport's key talents and are proud that the championship leaders recognise this.
"However, Williams has its own ambitions and we must always ensure we give our team the best opportunity to move forward. Any changes would only be made if Williams remains in a strong position to compete and develop in 2017.
"If we did allow Valtteri to leave, we would only do this if an experienced, credible alternative was available, such as someone like Felipe Massa, for example."
Williams, who finished fifth in the championship in 2016, have rejected Mercedes' first offer for Bottas, but talks are ongoing.
The team are playing hardball with Mercedes F1 boss Toto Wolff because he is in a difficult position having to find a team-mate for Hamilton when all the leading names are under contract.
However, it is a sensitive situation because Williams use Mercedes engines and want to keep a good relationship with the German manufacturer.
And now Mercedes have expressed an interest, Bottas is keen to take up the opportunity to join a front-running team.
Mercedes said on Thursday that they would not make an announcement on Rosberg's replacement until at least 3 January.
ncG1vNJzZmivp6x7o67CZ5qopV%2BovbC%2B02idqKqdqrmifY5sb2xrZWaDeg%3D%3D