The McLaren seen in Barcelona last weekend was effectively a 'B' model, according to Christian Horner.
Championship leader Sebastian Vettel was run hard to the chequered flag in Barcelona by Lewis Hamilton, despite the McLaren driver expecting to be much more easily beaten in the Spanish Grand Prix.
"We knew it would be a close battle," Red Bull team boss Horner is quoted as saying by Finland's Turun Sanomat.
"It would be very presumptuous to believe we have a car that is one second per lap better. We just had a phenomenal qualifying.
"I stress that McLaren brought an enormous update to Spain -- it's almost a B-model," he added.