Red Bull are going to be powered by Renault until the end of the season, with Horner suggesting ahead of FP1 in Singapore that any story about their engine supplier after that was mere speculation.
But, after the conclusion of FP1, Horner stirred the pot himself by suggesting that Red Bull will have an announcement of their own to make in the midst of the McLaren-Honda divorce and switch to Renault engines.
“I think there will be another announcement fairly soon that won’t be with Porsche,” Horner told Sky Sports F1.
“We have a relationship with a motor manufacturer already and you don’t have to be a rocket scientist to work out what it is.”
Horner also insisted that Carlos Sainz is still very much part of Red Bull’s plans, despite his seemingly imminent move to Renault.
He added: “If anything happens with Carlos Sainz, he will be very firmly still part of the Red Bull organisation and family.”