A two-time F2 race winner this season, his first in the F1 feeder class, Doohan sits ninth in the championship with four weekends of racing remaining.
He is, behind Piastri, the most senior member of the Academy and would logically step into the reserve driver/Free Practice 1 role should his countryman leave the Enstone squad.
“I think it would be very difficult to turn down the opportunity, no matter what,” Doohan said when asked by Speedcafe.com if he was ready to step up.
“Luckily, I've had the opportunity to be able to have a little bit of experience.
“It definitely helped [having some time in an F1 car] rather than none, however, there'd still be a lot of learning, a lot of in-depth study to be able to make sure I was up to par with what would be needed to do that.”
Doohan's comments were made on the Thursday prior to the Formula 1 Hungarian Grand Prix, after which Fernando Alonso announced his departure from Alpine.
That has set off a chain reaction, with the Enstone operation announcing Piastri as the Spaniard's replacement a day later, only for that to be refuted.
Earlier this week, Speedcafe.com reported that negotiations that will see Ricciardo make way for Piastri at McLaren have begun, with an settlement negotiations beginning at USD $21 million.
Ricciardo has been linked with a number of drives next season, with a return to Alpine (for whom he drove when known as Renault) thought the most likely.
A single year, or potentially a two-year deal, could leave Doohan well placed to then graduate to Formula 1 at the conclusion of that contract.