McLaren says it has back-up plans if Fernando Alonso opts not to continue at the team next year.
Alonso's contract is due to expire at the end of the year and he has made clear that he only wants to continue with McLaren if it is capable of challenging for wins in 2018. Much of that will depend on the competitiveness of the power unit in the back of the car, with McLaren currently attempting to negotiate a split with Honda and a move to Renault.
Asked what would happen if Alonso decided not to continue at McLaren next year, Brown said: "We've got another plan.
"He hasn't signed with us yet, negotiations are ongoing and going very well. But you've got to have a Plan B and C in the event that you don't reach an agreement, and we've got those plans."
Alonso has been particularly critical of Honda in his two and half seasons using the Japanese manufacturer's engines, but McLaren executive director Zak Brown insists the Spaniard has not been trying to influence decisions behind closed doors.
"Fernando's not giving us any ultimatum [over Honda]," Brown said. "All he wants is a competitive car. I'll be spending more time with him and these decisions can be based on whether he thinks we're going to be competitive or not. He's not going to be engine-specific in his desires."
Alonso's other options in Formula One appear slim, with the top three teams all set to continue with their current driver line-ups next year and the possibility of a switch to the Renault works team now looking less likely. He has been linked to a move to Williams for next year, but it is unlikely such a switch would result in the race wins Alonso desires.
One option open to McLaren if Alonso does leave is for junior driver Lando Norris to make the jump from Formula 3 to F1 following a successful test in Hungary earlier this year. But Brown said the current plan is for Norris to progress to Formula 2 before F1.
"Our current plans are to put him in Formula 2," Brown said. "Certainly I think he's fast enough to be in Formula One, but you need to make sure not to rush things and give him enough experience. So he's definitely our star of the future and I don't think we'd put him with another Formula One team."