Williams chief Frank Williams says his team must make an "imminent" decision on its engine plans for the 2010 season.
Williams, currently using Toyota engines, was believed to be interested in a deal with Renault, but a possible agreement was delayed by the French squad's involvement in the race-fixing scandal. Now the Grove, UK-based team is still considering its options, but Williams has made it clear that, from a technical point of view, the decision must be made very soon.
"You've got to get on with it and make up our minds – it must be imminent," said Williams.
"It's a technical choice and it requires a thorough vetting and consideration period by Patrick [Head] and Sam [Michael] plus some negotiations by Adam [Parr] once it's decided. We have to hurry up because we don't want to get behind on designing our car."
When asked if people get excited at the idea of Williams-Renault, the team boss said: "Absolutely." Williams also suggested Cosworth was still possibility.
"Cosworth is an independent company. The warmth that a manufacturer's engine provides is a useful feeling," he said.
Red Bull boss Christian Horner said his team, using Renault power units, was in a similar situation.
"We're in a situation where we need to get off the fence in the relatively near future, but nothing is fixed at this point in time," Horner said.