Fernando Alonso says he no longer knows what to expect from race weekends after a difficult opening four races of the season.

McLaren's start to the year has been plagued by reliability issues with its Honda power unit, resulting in three DNFs and two DNSs between the two cars. Aside from the reliability problems, the Honda power unit also has a significant performance deficit to its rivals, but Alonso says the focus has to be on reliability first.

"After a run of difficult races for us, I'm not sure what we can expect from this weekend," Alonso said. "We're expecting some various new parts -- which we bring to every race -- but we can't really focus too much on performance until we have solved our reliability issues. That's always our focus.

"I know the team is working extremely hard to get to the bottom of our recent problems, and I am hopeful we can have a smooth race and a weekend with very few issues. For me, qualifying has been an exciting session in the past few races and I hope we can repeat that in Barcelona, but the most important thing will be to maximise whatever grid slot we achieve on Saturday, on race day."

Despite the updates to the car this weekend in Spain, McLaren racing director Eric Boullier says there is no reason to expect a big leap forwards.

"While the start of the year and the first round of fly-away races have not been easy for McLaren-Honda, we're looking forward to returning to the Circuit de Barcelona-Catalunya for the Spanish Grand Prix, marking the start of the European leg of the season," he said.

"We don't anticipate a huge change of fortunes at this race, but getting Stoffel to the end of the grand prix in Sochi was a small reward for all the hard work being put in behind the scenes to address our reliability issues, and hopefully a sign of more positive things to come for the team.

"Like the majority of teams, we'll be taking this opportunity to introduce some new elements to the car, and, with the enthusiasm of the Spanish fans behind us, I hope we'll be able to complete some solid running and see an improvement in our reliability. It would be good to kick off the European races with some positive momentum, and what better place than in Spain with the full support of the passionate Spanish crowd."