In addition to the works outfit McLaren, the German marque also supplies engines on a commercial basis to Force India and Brawn.
Recent speculation suggests Red Bull, currently powered by Renault's V8 engine, is in negotiations to also use the Mercedes unit beginning next year.
Haug, Mercedes' competition boss, said the marque is keen to utilize the new FIA rule allowing a manufacturer to supply up to four separate teams because it is a way to make money.
"We could have three customer teams (in 2010), that's the plan," he said in Germany.
While Force India began a five-year engine deal this year, Mercedes wants to extend Brawn's single-season contract and then add another team to the roster in 2010.
With all of the three new entrants having signed Cosworth contracts, Haug would not confirm that Red Bull is the additional team in talks.
Sir Frank Williams, meanwhile, said at the Nurburgring that he is neither tempted to switch from Toyota or pen a low-cost Cosworth deal.
"I cannot mention any team names," Haug insisted, "but the positive thing is that we get quite a few requests actually. Our engine is seen to be a strong one, probably the best one."