Ferrari were quickest in pre-season testing at Barcelona's Circuit de Catalunya, however.
Team boss Mattia Binotto said Ferrari were "pushing hard to make up ground.
"We will have a new power unit that we are introducing ahead of schedule, as the second specification was due to be brought to Canada," he explained in a team preview of Sunday's race.
"It's only down to a big team effort with everyone pushing hard to make up ground that we have been able to bring these developments forward."
The Spanish Grand Prix is the first round of the European season with teams close to their factories again and set to bring some substantial upgrades.
"We are currently behind in the championship and we have to catch up, which we know means that our development work will be the key to this season," said Binotto.
Ferrari took a new aerodynamic package to the previous race in Baku, with Sebastian Vettel finishing third and Charles Leclerc fifth.
Vettel is 35 points behind Bottas in the drivers' standings. Ferrari are 74 behind Mercedes in the constructors' championship.
(Reporting by Alan Baldwin in London; Editing by Hugh Lawson)
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