With teams starting with a clean slate in 2017 following F1's regulation change, and the emphasis on chassis design, an area particularly suited to the genius of Adrian Newey, Red Bull is viewed as Mercedes' main challenger for the upcoming campaign.
But Horner says that a lot will depend on Renault's ability to deliver the goods on its end when it introduces it all-new power unit.
"They [Renault] are working very hard," said Horner.
"If they can make the kind of gain that they made last winter, over this winter, then with the stability of the rules, hopefully that [power] convergence will start to happen."
Horner insisted however that there was no real point in making any projections until the team's performance could be compared on a relative basis to that of its rivals.
"And, with the chassis hopefully playing a bigger role in the package, it may balance things up slightly. But it is all hypothetical as you don't know what everybody else has.
"All we can do is focus on the best job we can and worry about the others when we see them in Melbourne."