Red Bull team principal Christian Horner labelled Mercedes' new car as "extreme" but insisted it "ticks all the boxes" as a legal design.

Mercedes unveiled their W13 car on the first day of the pre-season testing session in Bahrain, with their new design featuring minimalistic vertical sidepods on either side of the cockpit.

Horner, who regularly battled with the world champions last season, reportedly told German outlet Auto Motor und Sport that the car was "not legal", but he has since clarified his comments.

"I think comments have been quoted that certainly weren't made," Horner said at Friday's news conference. "The car is obviously innovative, it's an interesting solution.

"As far as we're concerned it looks like the Mercedes car complies with the regulations. It's just a different interpretation, a different solution."

Horner was also quoted as suggesting the 'no side pod car' breached the spirit of Formula One rules, but the 48-year-old believes his words were misconstrued once more.

"There's not really anything that defines the spirit of the regulations, it either complies or it doesn't," he added.

"That's not really for us to judge, the FIA have the access to all of the drawings for a design like that which would have been submitted in advance. It's an interesting concept, it's a radical concept."

While impressed with the concept, Horner wants to wait and see whether it aids Mercedes on the track.

"Is it quick or not? Only time will tell. It's impossible to draw any conclusions other than it looks very different," he continued.

"Visually it is quite a departure from the concepts that certainly we've taken and a few others have taken.

"That's not to say it's naturally better or worse, it's just a different interpretation and compromises have been made with their layout to accommodate that."

Mercedes will look to defend their title at the start of the new campaign, which gets underway in Bahrain on March 20, but Horner believes Ferrari will be the team to beat in 2022.

"For me, the car that looks most settled on the circuit is the Ferrari," Horner said.

"I think they've had a very strong testing period so far, both in Barcelona and in Bahrain. They've looked extremely competitive whenever on track.

"But you have to remember these cars are still very immature, the rate of development will be very fast and intense. Mercedes are going to be a huge factor in this championship, I have no doubt."