Red Bull still considering line-up options

Both David Coulthard and Klien are both without a contract for next season, and Red Bull have been linked in recent months with several drivers, including McLaren's Juan Pablo Montoya and Renault tester Heikki Kovalainen.

But Horner said in Montreal that they are still looking around for the best two drivers they can have and did not rule out either Klien or Coulthard - although he admitted it was far from certain both would be retained.

"It is probable that we will continue with one of our current two drivers," he said. "The driver market is pretty fluid this year, and I think during the next month several pieces will fall into place.

"Obviously Red Bull are an attractive team. We are a team that are obviously going places and therefore there is obviously a very healthy amount of interest from a lot of drivers.

"Ultimately, we want to have the best two drivers in the car that we can. I think a Red Bull Racing-Adrian Newey car should be a step forward, and we will be looking at the best line-up we can in the car.

"If that is one of the two drivers from this year, or both, I cannot tell you today. But I think we are in a reasonable position and we will wait and see how things unfold."

The most likely outcome is that Klien will be forced to make way for another driver. Horner said that the Austrian needed to up his game if he was going to have any chance of staying.

"Christian is in his third year of F1 and he is not a rookie any more. He has got a very experienced teammate in David and he needs to tidy up elements of performance - like his inconsistency, and so on.

"He is working hard on that, so we will see."