Eric Boullier has admitted that he is not sure Fernando Alonso will stay with McLaren-Honda beyond the end of 2017.
Everybody in F1 expected that - in year three - the Anglo-Japanese works collaboration would finally start to bear fruit.
Yet McLaren-Honda kicked off Barcelona testing last week amid more technical and performance problems.
Asked what the mood is like behind the scenes, team boss Boullier told La Gazzetta dello Sport: "There are ongoing discussions.
"We are all disappointed by these first tests, because we could not do what we wanted. I do not know if Honda can give us the guarantees we ask for.
"But we absolutely need to see significant progress."
It is clear that the biggest problems are being suffered by Honda, who redesigned the power unit for 2017.
"The oil tank is fixed, but what worries me now is the problem of the second day," Honda's Yusuke Hasegawa told Spanish broadcaster Movistar.
"It could affect the start of the season, but I hope not and that we can be reliable in Australia."
If not, one domino that could eventually fall is Alonso, although the media has been expecting the Spaniard to implode long before now.
"After six months everybody said it would be a tragedy with him, a mess, but in the third year he is still here," Boullier said.
"Of course he is not happy, because he wants to fight to win. It is up to us to bring McLaren to the level it deserves."
Asked how he is managing to keep Alonso calm, the Frenchman answered: "By always telling the truth and avoiding wrong expectations. He knows the situation exactly."
The Spanish sports newspaper AS reports that F1 engine guru Gilles Simon has stopped working as a consultant for the Honda project.
As for whether Alonso will still be at McLaren-Honda in 2018, Boullier admitted: "I hope so, but I'm not sure.
"For sure Fernando is still at the top. The way he has prepared for this season is incredible. He is an example and an inspiration for many drivers."
The 2017 season gets under way with the Australian Grand Prix on March 26.
