Pirelli has questioned whether a plan to introduce a ban on tyre warmers in Formula 1 is going to be possible for next year.
F1's official tyre supplier will begin testing of new concept rubber in the post-Bahrain Grand Prix test next week with a view to preparing for a heating devices ban in 2015.
But Pirelli motorsport director Paul Hembery says that there are big safety issues in trying to find solution with the current dimension of F1 tyres.
"Working with no tyre blankets is a very big problem," he explained. "It is not an issue with the compounds, it is more to do with stopping a tyre becoming a balloon, and becoming undriveable or dangerous.
"That is the biggest issue we are looking at. At the moment, I have to say it looks very difficult to achieve for next season staying with the current tyre sizes."
Previous attempts to introduce a tyre warmer ban in F1 have been ditched on safety grounds, because of the difficulties of ensuring a minimum pressure limit.
Hembery said that if the F1 tyre size was different a tyre warmer ban could be introduced, but such a major change is not realistic for 2015.
"Everything is possible given time," he said. "The number of parameters involved are so important and so intrinsic to the inherent safety of the sport that it is not something that you can do lightly.
"While we do have an improved situation in regards to testing, it is debatable about whether or not that is acceptable or sufficient to allow us to arrive at a solution that is robust enough for F1."
He added: "There are other sports where you don't have tyre blankets, which is certainly true, like GP2 for example.
"But there are also a lot of other sports where the dimensions of the tyres are different, the starting pressures are dramatically higher, and you are looking at well over 20PSI.
"It is something that has been evolved over time; it is not something you do instantly.
"It is something that you have to do with caution, otherwise you think you are making a positive step but it can turn negative. So we have to make sure that it is a win/win for everyone involved."