Lewis Hamilton is facing a possible grid demotion after breaching a sporting regulation in morning practice at Interlagos on Friday.

The British championship leader, along with Jenson Button (Honda) and Takuma Sato (Super Aguri), will all be investigated by the stewards after the afternoon session for allegedly breaching article 25.3 relating to wet weather tyres, BBC Radio Five Live said.

It is claimed that the trio used two sets of wet tyres on Friday morning, where the rules say only one set may be used.

Article 25.3 reads: "No driver may use more than one set of wet and one set of extreme weather tyres during P1 and P2".

BBC Radio said a demotion of five grid positions is a possible sanction, but the stewards may also consider a solely monetary penalty.

With just Sunday's Brazilian grand prix to go in 2007, Hamilton is four and seven points ahead of Fernando Alonso and Kimi Raikkonen respectively in the drivers' classification.