Daniel Ricciardo is hopeful he can nurse his fourth engine of the season to the end of the Spanish Grand Prix to avoid a grid penalty in Monaco.
Red Bull were forced to install a new engine in Ricciardo's car in first practice on Friday after identifying a fluid leak.
Using a fifth engine would see Ricciardo incur a grid penalty that could see him start near the back of the field in Monaco in two weeks' time.
And Ricciardo, who only managed four laps in second practice on Friday, said: "We expected today to be limited with mileage.
"The main thing is to try to get this engine to the end of Monaco.
"That's the last place you want to take a penalty, so fingers crossed this engine lasts at least two weekends and then we'll assess everything after that.
"We've got to save mileage so we wouldn't have done much more this afternoon - probably one more run.
"Unfortunately we have to be aware that I'm already onto the last one. It's not something we can ignore.
"We're doing what we can, and we hope this engine will get us through at least Monaco so we don't have a penalty on a street circuit."