Sebastian Vettel fears if the rain pours on Sunday as it did in qualifying, the British GP could be more of a "lottery" than a race.
The conditions at the Silverstone circuit on Saturday were so appalling that race director Charlie Whiting was forced to red-flag qualifying for more than an hour.
The session was halted during Q2, which once underway was topped by Vettel ahead of his team-mate Mark Webber.
However, the German was not able to carry that pace through to the final segment and eventually finished fourth, 0.453s off the pace.
"It could be a big lottery just like today with conditions like that," said Vettel.
"It will be a tough day. Now it's raining again and it's probably the same weather tomorrow. It will be a long race."
Vettel added that he could have been quicker in Q3 and posed a great threat on pole position had it not been for a few mistakes in the treacherous conditions.
"Unfortunately in the end it was quite difficult with only one lap when the conditions were probably best," he told Autosport.
"Not ideal for us in terms of traffic but the lap I had was clean. I had some mistakes. It's the same for all of us. Sometimes it works, sometimes it doesn't."
Alonso reigns in extended qualy