This year, McLaren paired with existing Indycar outfit Andretti to field Fernando Alonso in the Indy 500.
Yet with the team expecting to be more competitive in Formula 1 with Renault power next year, it is believed that a follow-up project in 2018 is unlikely.
"If I remain in Formula 1 it's because I believe I can win next year," said Alonso.
"So I will be in Monaco because I don't want to lose any points there."
As for a full-time McLaren entry in the full Indycar championship, executive Brown played down that likelihood for now.
"We need to make sure when we get involved in activities beyond our formula one programme that it doesn't detract from our Formula 1 efforts," he said in a teleconference.
"Second, we have to be competitive, and third, it has to be commercially viable.
"With all that we have going on right now, spending much time thinking about Indycar would detract from our Formula 1 efforts, so I'd say we're years away from fielding an Indycar team."
McLaren sit ninth in the constructors' standings heading into this weekend's United States Grand Prix.