McLaren driver Jenson Button fears his team is too far off the pace to be competitive this Formula One season after he and Sergio Perez finished outside the top 10 in Friday's practice session at the Spanish Grand Prix.

Button was the only driver to fail to set a time in the rain-hit morning session. When the weather cleared in the afternoon, the 2009 F1 champion posted the 12th fastest time, one place above Perez.

"We're still a hell of a long way off the pace," Button said. "I think you'll see four teams that are very competitive at the front (in Sunday's race). I don't think we'll be one of them."

Button was angered by Perez's aggressive driving in the previous race, at Bahrain, as the team struggled for points.

After coming third in last year's constructors' standing, McLaren is languishing in sixth place this season with only 23 points from four races.

"Even if we make an improvement it's very difficult to make a big jump," Button said. "We don't have the outright pace of the quick guys. We need a big chunk (of improvement) and I'm not sure we have that."

It was hoped that upgrades to the car in Spain would improve its competitiveness, but those expectations have so far fallen short.

McLaren worked long into Thursday night on upgrades, even going beyond its curfew time, and parts were still arriving after Friday's first practice.

"We did have a lot of new parts on the car, visible parts on the car. I think we can improve overnight, but the thing is with this sport everyone's moving forward," Button said. "We need to work on some areas, areas I didn't think we'd have to."

Results so far have been poor: no podium finish, no grid position higher than seventh and no result better than fifth — Button in China. The swing into Europe is usually a good indicator of what's to follow for the rest of the campaign.

Perez's best result this season was sixth in Bahrain. Before that, he finished ninth and twice came 11th. Button has struggled just as badly: ninth in Australia, 17th in Malaysia and 10th in Bahrain.

With the way things look, even a top-10 qualifying result could prove difficult on Saturday.

"With getting the right set-up with the car, we'll see some improvements — but not to be fighting at the front," Button said. "I think it's going to be quite a big gap to the front."

It's some contrast to last year, when Button won three races and finished second three times.

McLaren's continuing concern is the correlation problem, similar to what Ferrari went through last season, with wind tunnel testing and data analysis still at odds with what's happening on the track.

"I think we need to keep working with the correlation. Once we get that right we can start to improve the cars in big steps," Perez said. "(But) we need a perfect weekend to be able to score some points."

There have been other concerns, too.

Button and Perez had to clear the air between themselves and with their bosses after their Bahrain clash in which Perez twice bumped into Button.

Perez is one of the most daring drivers in F1, but the Mexican is resigned to setting his sights low.

"At the moment it's not realistic to think we're going to be fighting for the title," Perez said. "It's the fifth race and we're still two seconds a lap slower."