Max Verstappen was victorious at the Albert Park circuit after a chaotic race with three red flags.
Sainz was given a five-second time penalty for making contact with Aston Martin's Fernando Alonso (41) at the second restart. With the race ending under a safety car, that sent him from fourth to 12th in the final standings.
"I think it's the most unfair penalty I've seen in my life," Sainz told reporters.
"I prefer to go back and talk to (the race stewards)... and maybe then I can come back and talk."
"I think it's too unfair and I don't feel well (enough) to speak."
Earlier, Leclerc crashed out on turn one of the first lap after making contact with Aston's Lance Stroll (24). Race officials determined no further action would be required.
"That's it, Lance touched my rear right wheel," said Leclerc, the winner of last year's race in Melbourne, on the team radio.
After finishing second in 2022, Ferrari sit fourth in the constructors' standings, almost 100 points behind Red Bull and adrift of Aston Martin and Mercedes.
