Still recovering from appendicitis surgery, Sainz won the Melbourne event after overtaking polesitter Max Verstappen on lap 2 as the Dutchman hit trouble with his brakes.
After Verstappen retired on lap 4, Sainz comfortably had the measure of Ferrari team-mate Charles Leclerc to take his first win since last year's Singapore GP, being the only driver other than Verstappen to win a race since April last year.
Sainz will lose his Ferrari seat to Mercedes man Lewis Hamilton in 2025, making him the most high-profile free agent on the driver market.
Most talk about Perez's potentially vacant seat, which is up for renewal, has centred around Red Bull's own drivers Daniel Ricciardo, Yuki Tsunoda and even Liam Lawson.
But amid rumours Aston Martin's Fernando Alonso might also be in the frame, Horner has given the firmest indication yet that Red Bull is willing to look outside its own driver pool.
"I think we want to field the best pairing that we can in Red Bull Racing and sometimes you've got to look outside the pool as well," Horner said, before referring to Sainz: "You've had a very fast, unemployed driver win today’s race. So the market is reasonably fluid with certain drivers."
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Sainz is also a previous Red Bull product, partnering Verstappen, Daniil Kvyat and Pierre Gasly at Toro Rosso between 2015-17, until an early move to Renault towards the end of 2017.
When pressed by Autosport regarding whether Horner would consider taking Sainz back, he replied: "Look, based on a performance like that you couldn't rule any possibility out, so I think you just want to take the time [to decide].
"Obviously, Checo was compromised today. He's had a great start to the season too, so we're not in any desperate rush.
"Carlos is the only driver that's beaten Red Bull in the last [year], so he appears to be our nemesis."
When asked if a performance like his in Melbourne, coming just two weeks after undergoing surgery for appendicitis, had raised his value, Sainz replied: "I don't know. For sure, it does no harm. That is 100%. I'm still without a job for next year, so I guess this is going to help it.
"I think everyone knows more or less what I'm capable of doing.
"I don't race to prove my value to team principals or to people. I race to prove to myself that if I'm given a car, I can get it done and I can be up there. And that's the mentality and the approach that I have and I will keep having the rest of the year."
