Hamilton and Mercedes have both insisted all seasons that a new deal is a formality yet it remains unsigned.

Red Bull team principal Horner has now prodded his rival team by calling out the stalemate in negotiations.

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“It’s strange because we keep being told, and I keep seeing in the media, that it’s just a matter of days,” he told talkSPORT.

“That’s been going on since February!

“So one can only assume that there is something fundamental that they can’t agree on.

“We don’t tend to conduct negotiations through the media.

“It is usually a couple of conversations around the table, and the job is done. So I don’t understand why.

“There has to be something preventing it happening.”

Hamilton has been linked to Ferrari while he has been negotiating the extension to his deal with Mercedes which expires at the end of this year.

Horner was asked if Hamilton and Max Verstappen could co-exist as F1 teammates.

“That’s like saying ‘could you have two centre-forwards playing for your favourite football team who are both hugely competitive and talented’,” he replied.

“It would be unrealistic to put both in the same team.”

Verstappen has prevented Hamilton from achieving the all-time record eighth F1 championship.

But Red Bull, who are set for another constructors’ and drivers’ double victory this season, recognise Hamilton’s legacy.

“Huge respect for Lewis,” Horner said. “He is the most successful driver of all time.

“He is a rival but there is respect for everything he has achieved.”