The 2009 Formula One world champion, who won last year's final race in Brazil, has finished no higher than fifth in four grands prix so far this season with a car that has been off the pace of the leaders.
McLaren principal Martin Whitmarsh said last month that the Spanish Grand Prix updates had to deliver a real performance improvement in Barcelona if the team were to stay in the championship reckoning.
"It's been difficult for the team to make consistent progress in the first four races," Button said in a team preview on Friday. "But I think returning to a circuit where we undertook two of the pre-season tests will give us a useful benchmark of our progress so far.
"There's been a lot of talk about the importance of next weekend's upgrades," added the 33-year-old. "But, as with every upgrade, they're simply part of the series of continuous improvement that are made across the season.
"There'll be elements of it that work, elements that perhaps work in a different way to what we'd anticipated and elements that don't work or perhaps require further work...so I'm pragmatic about what we'll discover next weekend."
Button, who was highly critical of his Mexican team mate Sergio Perez after a wheel-to-wheel duel in the previous race in Bahrain, remained hopeful that McLaren would be closer to the front than before at the Circuit de Catalunya.
Rivals also expected that to be the case.
"We know McLaren are going to bounce back, they've got a huge amount of resources, they don't lie down," Force India's Paul Di Resta said in Bahrain after finishing fourth to put his team ahead of McLaren in the constructors' standings.
McLaren are sixth with 23 points while Force India have 26. Champions Red Bull lead the standings with 109.
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