McLaren boss Zak Brown says the team has entered a crucial decision window with Honda, the end of which will make or break the relationship between the two partners.

In an interview with Reuters, Brown confirmed that an engine upgrade anticipated for this weekend’s Canadian Grand Prix has been delayed, taking down the Woking-based outfit’s hopes of a step forward in performance.

“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.

“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.

“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.