Michelin and Cooper Avon have emerged as the leading contenders to become F1 tyre supplier for the 2011 season.

Bridgestone will leave the sport at the end of the current season, with Michelin and Avon having both confirmed plans to try and secure a deal, with Michelin having initially appearing to be the favoured option with the competing teams.

However, Cooper Avon has now produced a proposal which would provide tyres at a lower cost, which has proved to be a major topic of debate for the teams.

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"The conversations really, at this point, are between Michelin and Avon," Williams technical director Sam Michael told the BBC. "Avon is a lot cheaper but it's a less proven product although they've done plenty of highly competitive tyres.

"They are a bigger unknown than Michelin because Michelin did it (in F1) very recently. But there is a significant difference in cost and you are probably talking over three times the difference in cost to the teams. So that's what's being debated at the moment."

Ferrari team boss Stefano Domenicali had suggested that an announcement could be made in time for next weekend's Spanish GP at Catalunya, but Michael said it was unlikely that a decision would be taken before the first European race of the season.

"I think the discussion in FOTA is just acknowledgement that you've got to take into account a lot of different factors, it's not a straight financial decision and it's not a straight technical decision," he added. "All this needs to be discussed with Bernie as he's traditionally looked after tyre supply."

Pirelli has also expressed an interest in making a return to F1.