Although Verstappen’s recent run of strong form to become the highest-scoring driver from the past four races has left Mercedes believing he is a title threat, Horner is not so convinced.
He believes the comfortable 69-point advantage that Lewis Hamilton holds over third-placed Verstappen, with just nine races remaining, means that his team’s title dreams are not realistic.
“Lewis has close to a three-race advantage with nine races to go, so he would have to not turn up for three races,” said Horner, when asked by Motorsport.com about his team’s championship prospects.
“It is hugely unlikely. They [Mercedes] would have to f**k up by gargantuan proportions not to win this championship.
“I think our target in the second half of the year is very much to close that gap. And as we get more performance on the car as Honda continues to make progress, this is very much a building year as we transition into 2020.”
Horner says that progress with the Red Bull car has been rapid since an update introduced at the Austrian Grand Prix helped improve the car’s balance and bring confidence to its drivers after a tricky start to the campaign.
“I think that the regulations change over the winter definitely did hurt us with the way we worked the front wing,” said Horner.
“But I think as the team have gained more understanding and have been able to use these new regulations better, we have been able to recover balance and characteristics of the car.
“Of course, that was combined with a tyre construction change as well, and those two elements hit us quite hard on the chassis side over the winter.
“But I think definitely we have made really good progress there in the last few months and hopefully with the development we see in the second half of the year, we have got a good vein of development that should continue to develop that.”