Ferrari may leave McLaren trailing in Valencia this weekend
McLaren believe the aerodynamic upgrades Ferrari are planning to take to Valencia this weekend could give the Italian team a clear advantage.
Ferrari have confirmed they will be introducing Red Bull-style exhaust outlets at the Spanish circuit.
Some believe the resulting aerodynamic gain is worth half a second a lap.
McLaren engineering director Paddy Lowe said: "There is a concern. It's a shame others [teams] have been slightly quicker to get it ready to race."
The design of the exhaust outlets used by Red Bull make the air and gasses flow through the car's diffuser and around the rear tyres more quickly and efficiently, reducing drag and markedly improving lap times.
As the extent of the advantage has become clear, other teams have been designing and testing their own 'blown rear end' systems, and Ferrari appear to have won the technological catch-up race.
Lowe confirmed McLaren will not be introducing the system on the cars of Lewis Hamilton and Jenson Button until the British Grand Prix at Silverstone in two weeks time.
"We're not promising a massive step in terms of a car upgrade [for Valencia], most of our effort has gone into making the best of this circuit," he acknowledged.
"I know a number of teams are introducing big changes, but we're not one of those. We'll have a bigger package for Silverstone."
He continued: "I agree with the maths [regarding the lap times], but we are where we are, and we'll just have to see what we can do at the weekend.
"But while the maths makes sense, each circuit has different characteristics, which suit some cars and not others.
"We saw Ferrari really struggle in Turkey, so I can't predict as an overall package where they're going to end up, any more than I can predict where we'll end up."
Although Hamilton and Button finished first and second in Montreal two weeks ago, Fernando Alonso's close third was an indication of Ferrari's increasing competitiveness.
If the aerodynamic upgrade is as successful as wind tunnel tests appear to suggest it will be, Ferrari could dominate around the Valencia circuit, which makes similar demands on the cars to those made in Canada.
McLaren appear to be less concerned about the fact their former chief engineer Pat Fry, who worked for the British team for 18 years, is to start work for Ferrari just six weeks after leaving.
"Pat was a great engineer and he'll do a great job for our long-time rivals, but we're not filled with great fear he's taken all our knowledge over there," said Lowe.
"Individuals can contribute, but they don't carry 'across the board' knowledge."