Former F1 driver Martin Brundle has claimed Sergio Perez has "lost his way" at Red Bull following a "snowball" build-up of issues.
Perez was once third in the drivers' standings, trailing team-mate Max Verstappen by just 15 points following his victory at the Monaco Grand Prix in May.
But the Mexican has since fallen 109 points adrift after struggling to match Verstappen's single-lap pace, with the Mexican driver finishing ahead only once of the current F1 champion in the last eight races.
In FP1 at Monza, Perez trailed pacesetter Charles Leclerc by 1.251secs and was 0.821s behind his team-mate.
Asked if a DRS issue could explain the full margin, Brundle told Sky Sports F1: "No.
"You could see it [the DRS] oscillating on a Red Bull. It can't be helped with the downforce but you don't need a whole lot of downforce there.
"What you don't need either is a whole load of drag, so if it's creating drag then it's slowing it down.
"Sergio has definitely lost his way a little bit with the Red Bull car at the moment."
Red Bull do not know Perez problem
The second seat at Red Bull is viewed as one of the most difficult to fill in F1 due to Verstappen being the clear team leader.
While Red Bull is committed to assisting Perez to escape his rut, Brundle added: "I'm sure if he knew, they'd sort it out very quickly.
"But it just doesn't seem to play to his strengths behind the wheel and then you lose a bit of confidence and trust on the braking point.
"And with these latest Formula 1 cars and the speed you take through these corners, if it starts sliding around too much, particularly at the rear end, and you don't hustle it then you lose a bit of tyre temperature and a bit of brake temperature.
"Then you get to a point where the car slides and you tighten up because, 'Oh no, the car is sliding,' rather than being just, 'Whatever, I can handle whatever you throw at me.'.
"It's a snowball effect of tiny little things and that's why it's hard to identify what has gone wrong and how to put it right."