"If it (the new car) is there and you can use it, you want to use it," team president Graeme Lowdon had said last week, sparking the uncertainty.
But Marussia told its 170,000 Twitter followers on Wednesday that its 2014 car will be at Jerez.
"For those of you asking if we'll be in Jerez next week ... we will indeed," the message read. "Can't wait to see the new MR03 out on track!"
The news puts the spotlight firmly on struggling Lotus, after boss Eric Boullier said he knew as "fact" that other teams will also be sitting out Jerez.
A table compiled by F1's official website showed that every team except Lotus has confirmed they will be testing with all-new V6-powered cars in southern Spain.
Lotus is yet to announce even a launch date for its E22.
Meanwhile, while Marussia ended its Jerez test announcement with the hashtag 'lookinggood', that was not the message given on Wednesday by Cyril Abiteboul, the Caterham team boss.
He admitted that the new green Caterham is "ugly", because of the solution used to comply with the FIA's new nose-height restrictions.
"Kids should be dreaming when they see a formula one car," he is quoted by Reuters. "I don't know what sort of dream or nightmare you will get when you look at those cars.
"It does remind me of (the film) Alien, with something coming out of the mouth and whatever. It's not very nice."