Ricciardo tested positive for coronavirus on Friday and is currently in isolation in Bahrain.
Though it is expected that the Australian will be able to return in time for the 2022 season-opener, McLaren has admitted it has backup drivers in mind just in case.
It comes in addition to McLaren's ability to access Mercedes' pool of drivers, offering the team an extra layer of security.
“In the spirit of offering maximum racing opportunities to our stable of young talent, we have agreed that McLaren may call upon BWT Alpine F1 Team reserve driver Oscar Piastri in the event one of their drivers is unable to race,” a statement from the team noted.
“Oscar will remain fully contracted to Alpine, and we will retain first options on his services.”
Alpine team principal Otmar Szafnauer added: “It would be great if Oscar can get some races under his belt in F1 and get that very valuable experience.
“We've talked to McLaren about Oscar being a reserve if they need him.
“He's definitely our reserve first and foremost, so if there was a conflict we would take him, but if Daniel can't drive then we'll offer him up.
“At least you don't have to change flags on the car, that saves a little bit!”
Mercedes' pool of drivers includes Formula E world champion Nyck de Vries, Stoffel Vandoorne, and Paul Di Resta.
However, both Vandoorne and Di Resta will be in action at Sebring for the opening round of the World Endurance Championship next weekend, ruling both out should Ricciardo be unable to drive.
Piastri is regarded as one of the brightest prospects not currently in Formula 1.
The Australian won last year's FIA Formula 2 Championship, having taken honours in the Formula 3 Championship the preceding season and Formula Renault Eurocup in 2019.
Tied to the Alpine Academy, there were few opportunities to move into an F1 race seat this season as the factory team had both Esteban Ocon and Fernando Alonso under contract.
Alpine (or Renault) does not have a relationship with another team at which it could place him in the interim.
He was briefly touted as a possible replacement for Nikita Mazepin at Haas, though that was quickly shot down by his management.
Opening practice for the Bahrain Grand Prix gets underway on Friday at 23:00 AEDT.
In the spirit of offering maximum racing opportunities to our stable of young talent, we have agreed that @McLarenF1 may call upon BWT Alpine F1 Team Reserve Driver @OscarPiastri in the event one of their drivers is unable to race. pic.twitter.com/etmryT1UrJ
— BWT Alpine F1 Team (@AlpineF1Team) March 12, 2022