The McLaren Formula 1 team will make a decision on its potential 2019 IndyCar project during September, says CEO Zak Brown.
McLaren confirmed on Friday that double F1 world champion Fernando Alonso will sample a 2018 IndyCar package for the first time on September 5, running on the Barber road course with support from Andretti Autosport as the two teams revive their partnership from the '17 Indianapolis 500.
Autosport had previously been told that McLaren's priority at present was confirming its 2019 F1 line-up, with Carlos Sainz Jr signed as Alonso's replacement but the call on the second seat yet to be made.
Brown says that McLaren's IndyCar deliberations will also consider whether it competes full-time in the series or just races in the Indy 500. It could still opt against racing Stateside at all next year.
"Fernando is testing next Wednesday in an Andretti car at Barber and that's for him to evaluate what an Indycar feels like on a road course," said Brown.
"From there he'll start to take a decision on what he wants to do next year and clearly, IndyCar is one of the series under consideration.
"We're very much doing the same and I think we'll make a decision sometime this month on whether we push forward with the Indy 500, IndyCar or doing nothing.
"Ultimately [there are] three decisions we need to make in September."
McLaren's IndyCar exploration has involved talks with both Honda and Chevrolet over an engine supply and Autosport understands the team is favouring Chevy.
That could be a potential complication for Andretti, which uses Honda engines.
Other McLaren options mooted include a takeover of the financially struggling Harding Racing team or a partnership with the Chevrolet-powered Ed Carpenter Racing (pictured), which recently described the McLaren situation as "fluid".
McLaren has approached both Penske's Will Power and Chip Ganassi Racing's Scott Dixon over a seat with its prospective two-car team, but both opted to sign new deals with their current outfits.
Despite the September deadline outlined by Brown, Alonso has previously stated he would not make a decision on his post-F1 future until "maybe October".
After winning the Le Mans 24 Hours earlier this year with Toyota, the Indy 500 is the only race left in Alonso's triple crown bid.
McLaren itself has also been open to racing in more categories, having kept an eye on the World Endurance Championship's LMP1 replacement concept.