Williams will find out by the end of June if they will still have exclusive rights to BMW engines or be forced to share their supplier with Sauber.
Williams have not won the F1 championship with BMW engines
BMW is in talks with Sauber, and there has been speculation it could buy the Swiss team and stop supplying Williams.
But BMW motorsport chief Mario Theissen said: "I can only say we are very focussed on working with Williams.
"We are talking to Sauber primarily on engine supply for next year. Everything beyond that is speculation."
Williams have had BMW as their engine partners since 1999, but have failed to win a world championship in that time.
A low-key start to the season was followed by second and third places for Nick Heidfeld and Mark Webber at the Monaco Grand Prix.
And Heidfeld gave the German company another podium in the European Grand Prix by finishing second at the Nurburgring on Sunday, having started the race from pole position.
"We will discuss our strategy in June. Don't expect a result next week, rather at the end of June," said Theissen.
"It is an internal discussion. As soon as we have a decision we will certainly communicate it."