But Red Bull's Christian Horner said after Sepang: "It's a big gap. They have plenty up their sleeve."
Ferrari's Fernando Alonso, meanwhile, acknowledged the Italian team is not yet even in a position to beat the second force of 2014, Red Bull.
"For Bahrain we can't expect any miracles, because we are practicing again in just five days and so no teams are going to make any sudden, giant steps," said the Spaniard.
"Top speed is also important in Bahrain and so I expect Williams to be strong as well. I want to be in the top five again.
"We need to keep finishing as close as we can to the top, so that we can think about the championship later on if the car is more competitive," Alonso is quoted by Speed Week.
As for McLaren, racing boss Eric Boullier was forthright when asked if the British team can close the gap to Mercedes for the start of the European season, when the first major development steps will be made.
"No," he answered.
Is Boullier confident the gap can be closed at all in 2014? "That's the right question," he added. "Maybe by Europe next year, yes."