McLaren is nearing a "fork in the road" in its Honda relationship, with executive director Zak Brown expressing "serious concerns" about the Japanese manufacturer's ability to recover from its current situation.
McLaren is rooted to the bottom of the constructors' championship having failed to score a point this season, mainly due to Honda's third consecutive failure to produce a competitive or reliable engine. Honda was due to bring an upgrade to the Canadian Grand Prix this weekend but looks set to miss that deadline.
After watching Fernando Alonso's bid to win last month's Indy 500 thwarted by a Honda engine failure, Brown said "all options are on the table". The American has hinted that the latest disappointment has tested his patience.
"Honda's working very hard but they seem a bit lost," Brown told Reuters. "We were only told recently that we wouldn't have the [Canada] upgrade coming....and we don't have a definitive timeline, which is concerning because the pain is great and we can't sit around forever.
"We were eagerly awaiting this upgrade as were our drivers and it's a big disappointment that it's not coming. It's not lack of effort, but they are struggling to get it to come together."
With rumours of a return to Mercedes power, Brown went on to say the next three months will be crucial to determining what is inside McLaren's 2018 contender.
"It will all come together. There's lots of things that go into the decision and we're entering that window now of 'which way do you go when you come to the fork in the road'."
Honda's progress between now and the second half of the season is also likely to dictate whether Fernando Alonso stays with the team or looks elsewhere for 2018. The Spaniard, who only decided to race at the Indy 500 because of Honda's current predicament, is in the third and final year of his contract and has made it clear his top priority is finding a car which can challenge for a third world championship.
Brown will not accept another situation which sees McLaren so far off the pace next season.
"The executive committee have now given us our marching orders. We're not going to go into another year like this, in hope. I don't want to get into what our options are. Our preference is to win the world championship with Honda. But at some point you need to make a decision as to whether that's achievable. And we have serious concerns.
"Missing upgrades, and upgrades not delivering to the level we were told they were going to, you can only take that so long. And we're near our limit."