Red Bull's top engineer says his team will have a tough year in 2023 after a dominating season where they won both world championships.

The Milton Keynes-based outfit will have their title defences hampered after breaching F1's cost cap in 2021 — when Max Verstappen won his first drivers' championship.

Red Bull were found to be marginally over the cap — $US145 million ($216m) — with miscellaneous expenses and a failure to lodge a tax break reportedly the main reasons for the breach.

Along with a financial penalty, Red Bull have had their allowed aerodynamic testing time for next season reduced by 10 per cent.

This means their rivals will be allowed more time to test their new cars for the 2023 season.

Adrian Newey, Red Bull's chief technical officer, said the penalty meant the team had to be very precise with the work they do in the lead-up to next year.

"The reduction in internal testing means therefore we can evaluate less different components, less different ideas," he said.

"If we're really smart and always put the right things on the model, then of course it doesn't make much difference."

'Ferrari won't be resting'

Newey, who has designed every championship-winning Red Bull car, said he expected next year to be a difficult title defence.

He said Ferrari, who recently appointed Fred Vasseur as team principal, will identify their weaknesses in 2022 and be stronger in the new season.

"Ferrari won't be resting. They had a couple of reliability problems and obviously made a couple of more mistakes. So they will be right back," he said.

"You saw Mercedes starting with a car which was quite a long way off the pace, and evolving it to the point where they won [in Brazil].

Pre-season testing will be held in late February before the first race of the season in Bahrain on March 5.