Red Bull boss Helmut Marko has hit out at one of his star drivers over his 'unpredictable' form.
The reigning Formula 1 constructors' champions are in a fierce battle to retain their crown, with McLaren currently ahead in the standings with six races of the season remaining.
It's been a frustrating campaign for the Milton Keynes-based outfit, with both of their drivers suffering a dramatic drop-off in form despite each making a positive start to the year.
Defending drivers' title holder Max Verstappen continues to lead the way as he targets a fourth consecutive championship, but he has been placed under significant pressure by his McLaren counterpart Lando Norris in recent months.
Marko however, has now spoken of his frustrations over how the Mexican's up-and-down performance levels have allowed McLaren to take full advantage.
Speaking to Sport.de, the Austrian said: "We know that Pérez has fluctuations. Especially when the car is modified at short notice, he needs a longer time to adapt.
"That is certainly a factor why McLaren is currently stronger than us in terms of driver pairing.
"In terms of speed, he can do it. He just has fluctuations that are becoming more and more unpredictable."