Bottas finished eighth in the drivers championship last season, 32 points ahead of teammate Felipe Massa. Massa retired from F1 after the final grand prix in Abu Dhabi, and if Mercedes did poach the Finn, Williams would be left with just rookie driver Lance Stroll.
Wolff Aiming to be Brave
Several days ago, Mercedes boss Toto Wolff vowed to make a brave decision as he looked to replace Rosberg for the 2017 season.
Rosberg stunned the world of F1 when he retired just five days after winning this year's championship.
Wolff has been working overtime to line up a new driver to race alongside Mercedes star Lewis Hamilton next season and, with pre-season testing due to start in February, he wants the situation sorted out as soon as possible.
Two-time world champion Fernando Alonso, entering the final year of his three-year deal with McLaren, had been linked with Mercedes, as had Bottas.
"Clearly, with Nico taking the decision quite late we are in a bit of a compromised situation because if we had known three months ago there were more options available," Wolff told Sky Sports F1 on Friday.
"Maybe we need to make a brave decision in the same way Nico has made a brave decision." Pascal Wehrlein graduated from Mercedes' young driver program and notched up Manor's only point of the season to underline his potential, and was in the running to partner Hamilton.
However, he was ignored for a Force India seat in favour of fellow Mercedes junior Esteban Ocon and is currently without a team for next year.
"Sometimes in life things turn out differently than you expected," Wolff said. "I think in terms of performance, both have had great races in the past, had solid performances with Manor, and they deserve a future in Formula 1.
"Therefore I consider both of them as future stars."
Whoever steps in for Rosberg will have big shoes to fill and Wolff admitted his unexpected departure was a big blow.
"He will leave a very big gap because he was not only a very fast driver, but he was able to push Lewis," Wolff said.
"They pushed each other and were therefore really able to perform well and score our goals for victories.
"His technical ability in giving us directions and being part of the development work of the car, that's a part we are going to greatly miss.
"Whoever is going to replace Nico needs to fill those big shoes."
Silver Arrows Face Second Shock Exit
Mercedes' technical head Paddy Lowe could also be about to follow Rosberg out the door.
Motorsport.com reports multiple sources "with good knowledge" indicating Lowe, who has helped Mercedes win three successive constructors titles, is set to join rivals Williams.
Mercedes, who were rocked by Rosberg's retirement only five days after winning the title at the end of last month in Abu Dhabi, had no comment on rumours rife since September.
Lowe started his F1 career with former world champions Williams in 1987 and spent six years there. The team finished fifth overall this year. Williams' current technical head Pat Symonds is 63 and told Reuters in a recent interview he would still be at the team next year, while also indicating he was looking to reduce his workload.
"I love motorsport and the engineering of it but it is relentless. It really is intense. I'm still working 60 hours a week and there comes a time when I'd like to do other things as well," he said.
Lowe's contract at Mercedes expires at the end of the year, according to reports in Britain and Germany, and the 53-year-old's future has been the subject of considerable speculation.
McLaren, his previous employers, last week ruled out a move for the Briton.
