Mercedes will not enter into discussions with McLaren about a 2018 engine supply unless it severs ties with Honda first.
McLaren and Honda's disastrous relationship has taken a turn for the worst in recent weeks, with McLaren boss Zak Brown publicly criticising the Japanese manufacturer after failing to bring a planned engine upgrade to Canada. McLaren is currently rooted to the bottom of the constructors' championship and trying to convince Fernando Alonso to stay for another year, though the Spaniard has made it clear he will leave unless Honda shows big signs of improvement before the close of 2017.
Former engine supplier Mercedes appears to be the only logical solution for McLaren if it does split from Honda, though the world champion's motorsport boss Toto Wolff wants to see Honda succeed with the Woking outfit and will not entertain the idea of a switch until that situation is resolved.
"There's quite some momentum in the market at the moment, which we watch from the sidelines," Wolff told the FIA Sport Conference. "This is a position we have put ourselves in because the most important thing is that Honda performs, stays in the sport and has a good deal with its customer teams or works teams. We wouldn't want to interfere at that stage, that is our priority.
"[Supplying McLaren] is not our priority at the moment. First we would like to see Honda and McLaren sorting out their relationship."
Honda has failed to deliver McLaren a competitive engine since returning to the sport in 2015 but has secured a second customer team for next season, with Sauber set to join. Wolff believes it would be wrong for Mercedes to interfere with Honda's business until there is a clear resolution to the McLaren situation.
"If you are being considered as the new bride you want the couple to divorce first before you jump into the bed. We tried her out for 20 years. The main priority is for Honda to stay in the sport and for Honda to have a functioning relationship with its customers. That's why at the moment we do not wish to dive into this topic."