Toto Wolff says Mercedes needs to know if McLaren needs a customer engine supply for 2018 sometime "after the summer break".
Although Honda made a step forward in Baku, it is increasingly clear that McLaren and Fernando Alonso’s patience with the hapless Japanese supplier is up.
"I think our opponents are even a bit confused about our speed," Spaniard Alonso said at Baku.
"We are so slow that they probably think we are going into the pits when we are actually starting a flying lap. I’m sorry, but it’s true," he added.
So rumours are rife that a McLaren-Honda divorce is in the works, with the British team lining up a Mercedes deal instead.
Mercedes boss Wolff says nothing is confirmed, but a deadline is looming.
"We would have to know something after the summer break," he said at Baku.
"McLaren probably needs to know earlier than we do, but I say again — we do not interfere in the relationship between Honda and McLaren.
"We will not be a reason for any divorce. Only if McLaren is at the point where they need an engine will we listen. We do not grab a partner away from another manufacturer," Wolff insisted.