Fernando Alonso could be an option for McLaren if either of their Formula 1® drivers are unable to race, according to team principal Andreas Seidl.
Alonso is still under contract with McLaren, having tested their car for 2019, while his last involvement with them was a failed attempt to qualify for the Indianapolis 500 earlier this year.
The two-time F1® world champion is expected to make another bid for the Indy 500 in 2020, while the Spaniard will attend the upcoming Italian Grand Prix at Monza as a McLaren ambassador.
Lando Norris sustained a foot injury ahead of last weekend's Belgian Grand Prix and, though he recovered to take part at Spa, Sergey Sirotkin was considered as an emergency replacement.
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Sirotkin is McLaren's primary reserve, but Seidl has revealed Alonso could also be called upon if needed, as long as there was sufficient time to make the decision.
"With Lando being clear that he felt fine to race, the back-up would have been Sergey [if Norris had been ruled out late]," he said in quotes reported by Autosport.
"It's a different situation if we know early enough, to look for alternatives. But it's something we discuss when it comes to that situation.
"Our reserve driver is Sergey, so we have the seat ready and everything, and we have prepared him in the simulator.
"I don't know exactly how the contract is exactly [with Alonso], but he is still a part of McLaren.
"Zak [Brown] is still having a lot of exchange with him and other programmes I'm sure. If we would have an issue like that [a driver being unavailable], there would be a discussion happening."
Despite Norris' timely return from injury, McLaren suffered engine failures in both cars during the Belgian Grand Prix.