Red Bull faces a race against time to give Mark Webber KERS capability in time for the Chinese Grand Prix qualifying session, after the Australian suffered more problems in final free practice at Shanghai this morning.
Webber managed just one flying lap in the final hour's practice after an electrical problem in the RB7's wiring loom meant that he was unable to activate his KERS on track.
The issues come after the 34-year-old was unable to use KERS through the Malaysian Grand Prix last weekend.
"There was an electrical issue, a wiring loom issue actually that caused some concern with the KERS," team principal Christian Horner confirmed to the BBC, who conceded that it was touch and go whether Webber would be able to use the system in qualifying.
"We are doing our best to try and make sure that it is in working order on Mark's car. It's going to be very, very tough though. It looks like a few issues, so it's probable that we won't be running KERS on Mark's car in qualifying but we should be okay for the race."
Horner added that Sebastian Vettel, whose KERS is working correctly, was happy with his running during the morning session after the world champion set the pace in all three practice sessions.
"Sebastian seemed very happy with the balance of his car this morning," said Horner. "Mark, on the one flying lap that he had, was a lot happier today than yesterday, so hopefully we should be in good shape."