Rosberg, whose Williams contract expires at the end of the new season, has said it will soon be make or break time if he is to challenge McLaren's Lewis Hamilton for the title.

The 23-year-old has finished 17th, ninth and 13th in his three seasons behind a Williams wheel but Sir Frank admitted: "If Nico had a McLaren he would be running at the front all the time. He is rather good."

Rosberg has made it clear he would prefer to make his breakthrough as a podium regular by staying with the Oxfordshire-based team and a raft of new rules designed to make the sport more competitive could edge Williams closer to recapturing their glory days of the 1990s.

Asked if he feared losing Rosberg, Williams said: "It's something we have obviously thought about. We want to have a competitive car and time will soon tell if we have or we haven't."

Rosberg managed a second and a third last season but it is now five years since a Williams driver tasted victory.

Williams said: "If we get one win we will have to keep it rolling but for most teams on the grid every race is a mountain. I don't mean that as a cheap show of words, it is very competitive but that is what we want.

"If at the end of the year we look back and find ourselves close to the top three that would be a big step for year one. It is by no means impossible. We might get lucky with the car."

If Rosberg faces an uncertain future that is nothing compared to the worries of British driver Jenson Button, who controversially bought himself out of an agreement to drive for Williams in 2005.

Button's Honda team were closed by the Japanese parent company although hopes remain of a resurrection via a buy-out in time for the 2009 season curtain raiser in Melbourne.

Williams was hopeful there would be a Honda on the grid in four weeks' time, adding: "They are a bunch of racers I very much admire. They might make it, although I don't know the facts. I'm just guessing."

Williams chief executive officer Adam Parr was more confident. He said: "The fact that they are still talking is important because if Honda wasn't faced with any serious opportunity then they would have called it a day. So the fact that we are four weeks away from the start of the season and they are still making kit must mean that Honda are taking the proposals very seriously."