Christian Horner: "If we can be competitive at Valencia and Silverstone then the rest of the season looks promising" © Sutton Images
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Christian Horner believes Fernando Alonso is Red Bull's "obvious" rival in the fight for the title, but is expecting challenges for race wins from several teams.

Alonso currently leads the drivers' championship but Sebastian Vettel could have been on top had an alternator problem not forced him to retire from the lead of the European Grand Prix. Red Bull had the fastest car in Valencia two weeks ago, but Alonso, in a car that is still off the pace in qualifying, took victory.

Asked if there was a single driver he saw as Red Bull's biggest threat this year, Horner told ESPNF1: "The driver, obviously, is Alonso. But there are so many drivers that are in contention and teams as well. I think Formula One has never been so open as it has been [this year], going in to grand prix weekends where there could be eight potential winners."

Red Bull brought a major upgrade to the rear of its car at the last race in Valencia to enhance the performance of its diffuser. Horner is wary that Silverstone will provide a different challenge at this weekend's British Grand Prix, but said another strong performance would bode well for the car's chances at all venues this year.

"In Valencia the car worked very well, but that was in high temperatures and with a different type of layout. Hopefully it will follow through in to the next grand prix at Silverstone - it's a completely different layout of circuit with fast sweeping corners, probably cooler temperatures and knowing the British summer maybe a bit of rain. Hopefully the car can be competitive and if we can be competitive at Valencia and Silverstone then the rest of the season looks promising."