Sauber insist they are not talking to Mercedes amidst rumours they intend swapping engine suppliers for 2014.
Next season, Formula One's engine regulations will undergo a major overhaul as the sport swaps from V8s to 1.6 litre turbocharged V6s.
This has led to some reports claiming that Sauber could ditch Ferrari in favour of a move to Mercedes power. However, team boss Monisha Kaltenborn says her team has yet to make a decision.
"It's a very interesting situation for customer teams at the moment," Kaltenborn told Autosport. "There is so much, as we understand, that is not clear at the moment, so it's very difficult to engage into these kinds of talks.
"For us, we have had a partnership with Ferrari for more than 10 years, so that's the natural link for us to go. But they also have difficulties, because nothing has been clarified down to the last detail.
"It's extremely challenging, and a fear we have as a private team is to make sure we don't have any disadvantage compared to the manufacturer teams.
"It comes down to finding the engine, knowing the technical details of it and knowing what impact it has on our design."
Pressed as to whether she had held talks with Mercedes, Kaltenborn said: "Just to be very clear on this, we are not talking to anyone else, unlike what was reported."