McLaren are yet to make a decision on who will replace Fernando Alonso at the Monaco Grand Prix, despite Jenson Button forming part of a "three-driver" setup in their squad.
Alonso will skip the Monte Carlo showpiece in order to race for McLaren at the Indy 500.
In September last year, McLaren said Stoffel Vandoorne would partner Alonso in 2017, with Button in position to "be available to race for us if circumstances require it".
However, Button - employed as an ambassador by McLaren - intimated at the end of the 2016 season that he was retired and new chief Zak Brown says the veteran of 305 grand prix starts is not necessarily the man for the job.
"Fernando's replacement driver is not in place, those conversations are ongoing," Brown told a media conference.
"We have a few different options and we'll state who that is when we know."
Asked whether the in-season test following the Bahrain Grand Prix would offer a clue, Brown replied: "That's ultimately an Eric Boullier decision. He's not here [in Bahrain] yet.
"I believe Stoffel is going to be in the car for some of the time."