Stoffel Vandoorne will serve as McLaren's official reserve driver for the remainder of the 2020 season following the conclusion of the Mercedes driver's Formula E campaign.
The sudden unavailability of Racing Point's Sergio Perez following a positive COVID-19 test before the British Grand Prix prompted McLaren to put in place a contingency plan in case one of its drivers was unexpectedly sidelined.
McLaren relied on Paul di Resta as its reserve driver last time out at Silverstone, but from this weekend's Spanish Grand Prix the Woking-based squad will revert to its arrangement with future engine supplier Mercedes by which Vandoorne will embed with his former team as its back-up.
"At the moment our consideration is that we have an agreement with Mercedes regarding the use of their reserve driver in case there's the need on our side," explained McLaren F1 boss Andreas Seidl, quoted by Autosport.
"What was special [last] weekend is that Stoffel Vandoorne was simply unavailable because he is doing Formula E.
"But with Stoffel being available again from Barcelona onwards, that is our main direction."
Mercedes' second reserve driver Esteban Gutierrez is currently ineligible to race in F1 as the Mexican does not hold an up-t-date superlicence.
Vandoorne will conclude his season in Formula E with Mercedes later today at the all-electric series' final round in Berlin and then will fly to Barcelona to be on site for the weekend with McLaren.