And in pre-season testing ahead of the 2014 season, Marussia's new MR03 - powered by a Ferrari 'power unit' for the first time - looks considerably quicker than Caterham's struggling Renault-powered machine.
McLaren driver Button is quoted by Brazil's Totalrace: "It's interesting to see how some teams have improved their cars suddenly.
"There are several teams that are strong at the moment," he added. "Even Marussia -- their car is much better than last year.
"I think people will be surprised at how they are actually competitive," said Button.