Zak Brown says that McLaren is yet to make a decision about an engine deal for 2018, despite holding new talks with Renault at Monza.
Sky Sports News reported that Renault bosses Jerome Stoll, Cyril Abiteboul and Alain Prost held talks in the McLaren motorhome after Friday practice. They were joined by Formula 1 sporting director Ross Brawn.
But Brown says that the final decision is still to be made. He noted that the team has until mid-September to make its final choice between Renault and current engine supplier Honda.
"It is very complicated," he said. "There are a variety of pieces to the puzzle, some in our control, some not.
"It can still go either way. It's probably one of the biggest decisions McLaren have ever had to make.
"Negotiations are ongoing and they are going very well," he added. "But you have to have a Plan B and a Plan C in the event you don't reach an agreement. And we have those plans."
Cancelling the current arrangement with Honda could cost McLaren over £50 million in funding. But Brown insisted that that the money is pointless if it means McLaren isn't competitive.
"We can't afford not to be on the podium," he said. "We are here to win so we are going to make a sporting decision.
"The best thing for McLaren is to make the best sporting decision possible," he continued. "Fortunately we have extremely committed shareholders which means we can make a sporting decision and deal with the economics."
Another crucial element to the puzzle is the future role of Fernando Alonso. The team is desperate to retain the two-time world champion, but he's said he'll only stay if the team has a race-winning car in 2018.
"Fernando has not given us any ultimatum, that it's 'them or us', at all," Brown told Sky Sports. "His decision will be based on whether he thinks we will be competitive or not. He's not been engine-specific in his desires."