Jenson Button fears that his gearbox problem in Friday practice in Canada could prove costly given that it interrupted his planned long run.
A gearbox issue forced Button to park in the McLaren garage near the end of the day's only fully-dry session, curtailing his programme and leaving the team short on data.
"I think the pace today was OK, we were running different downforce levels in the second session which was interesting, it's just whether we're brave enough to attempt something like that with having only done a couple of laps on high fuel loads," Button said.
"The long-run information is really what I needed on my car, so it's going to be difficult to know what to do with the balance and set-up for tomorrow."
Button said the shortened running also had an impact on McLaren's development programme for Canada.
"We were trying something in that session which was quite interesting but we didn't get the information while running on high fuel," he said.
"I did three laps. It's very difficult to go into a race and you'd be very brave to put that part on the car, if you've only done three laps on it."
He admitted last year's Canadian GP - in which he slumped to the lower end of the midfield and was lapped by victorious team-mate Lewis Hamilton while struggling with tyre performance - is an experience he fears repeating.
"We had that issue last year when we had a gearbox problem and had a disastrous race because of rear graining," said Button.
"We needed to be reliable today, but we're running different set-ups on both cars so at least we got some information."