McLaren led the F1 constructors' championship at the start of 2014 following its double podium in the Australian GP with Kevin Magnussen and Button, but did not score in either Bahrain or China and is now 111 points behind leader Mercedes and fifth in the standings.
While a clutch issue ruled out both cars at Sakhir, it was a simple lack of pace that kept Button and Magnussen out of the points at Shanghai as they finished 11th and 13th.
Asked if he was counting on an upgrade package for Barcelona next month, Button replied: "Yeah we've got some upgrades, but we're a lot further behind than we were at the last race.
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"I don't think people brought that much [development parts] here, so I don't know what we're doing really.
"It's a disappointment for the team. When you work so hard and you have such a bad result like this it's tough, especially back at the factory, so hopefully they can stay positive and update the car because at the moment this isn't good enough."
Although Button and the team discussed electrical issues over the radio during the Chinese race, the Briton said that was not a factor in the result.
"No, we're just not quick," he said. "We had a few issues but I don't think they slowed us down."
He believes the main problem is a lack of affinity with the 2014 Pirellis.
"I think it's a little bit like in the wet, we can't get the fronts working," Button said.
"They just grain. We're maxed out on everything with the car, we're very high on the front wing , where we've never been before, so it's all very strange.
"Hopefully we'll solve it for the next race as it was pretty painful out there.
"I think the car is an alright car, but we can't get the tyres working and that's one of the biggest things in Formula 1 these days."
Team-mate Magnussen still thinks the car is very short on downforce.
"We lack overall grip," he said. "The car feels good but we just need loads of downforce."
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