http://www.bbc.com/sport/formula1/38335169
Valtteri Bottas: Williams open to Finn joining Mercedes
Williams are prepared to release Valtteri Bottas to become Lewis Hamilton's Mercedes team-mate in 2017.
Mercedes want the Finn, 27, to replace Nico Rosberg, who retired after winning the world title last month.
Deputy team principal Claire Williams told BBC Sport the team would let Bottas leave "if an experienced, credible alternative was available".
Williams suggested Felipe Massa could return, despite retiring at the end of this season.
"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.