Jenson Button fears Red Bull may have "stolen a march" on McLaren this season that has left his hopes of back-to-back world titles hanging in the balance.

Button goes into Sunday's Belgian Grand Prix just 14 points adrift of championship leader Mark Webber, but aware McLaren are playing catch up with Red Bull in terms of performance.

In particular, McLaren suffered a chastening experience in the last race in Hungary just under four weeks ago when they were trounced by their title rivals, and Button said: "Red Bull have stolen a march massively, and sometimes it can take a long time to catch up, especially when they have that much in hand around a circuit like Hungary."

He added: "It's very tricky and it does take a lot of time especially at this point in the season when everyone is so reliable.

"You're losing a lot of points if you don't have the parts."

The parts Button is specifically referring to regard their front wing and floor, which would appear to be working in tandem.

The Red Bull front wing appears to flex far greater than the regulations allow, so increasing the level of downforce and with it speed.

Although the FIA have ramped up their tests for this race regarding front wing flexibility, the team are far from concerned.

That has prompted the FIA to introduce further tests ahead of the Italian Grand Prix to look at the floor as it is believed that is somehow aiding the front wing.

Hinting at Red Bull's advantage, Button added: "Webber said in an interview a couple of weeks back that if you have a very special device on the car, people should have to try and build their own. I didn't know they had a device on the car, but there you go."