Marlboro Ducati's Casey Stoner has warned the Indy MotoGP may not go ahead if the rain continues, citing that the amount of standing water is too dangerous.

The out-going MotoGP Champion, who high-sided in yesterday's first free practice, also said he wasn't happy with the difference in grip levels between the old and new tarmac.

"The track conditions vary drastically between the old surface and the new. Grip is good on the old stuff but there isn't even minimum grip on the recently laid asphalt and the rain makes it much worse because it isn't draining off. If it continues to rain like it did this afternoon then I'm not sure the conditions will be safe enough to race in," he said.

"I crashed on the section where the grip is poorest and that's obviously not good for the wrist but thankfully it didn't create any major problems."