Jenson Button has admitted that it proving to be difficult to McLaren to fully understand its new MP4-28, despite Sergio Perez posting the quickest time at Catalunya earlier this week.

Perez was fastest on Wednesday to build on an encouraging first test for the new car at Jerez, with Button then seventh quickest when he got back behind the wheel of the car on Thursday.

Speaking to reporters following his first day of running this week, Button admitted that he didn't feel he was getting the best from the car, with the team needing to work to get more consistency from its 2013 challenger.

"It's been a very difficult few test days for me in terms of mileage," he said. "It's been very tricky to understand where the car is: at times the car feels good, at other times it doesn't. A lot of that is basically understanding the car that we have and making sure it's working as we expect it to be working.

"Some of the time that hasn't been the case, so that's why it's been a tricky winter so far. But as you can see there are times when the car's working pretty well. At Jerez we showed pace, we also showed that we didn't have pace at other times. We don't know where we are and there's no point trying to compare ourselves to other people. We've got to sort out our own issues and get the best out of the car that we have.

"In terms of laps completed and the testing that I have achieved, I think we're behind on that. And a lot of it has been because we've been doing certain tests that have taken a bit longer than we wanted and as soon as one change takes longer it rolls into the next change and then it's lunchtime. So most of our testing is done in the afternoon these days! So it's not been perfect and we know we've got a lot of work to do in terms of spending more time out on the circuit and understanding the car."

Expanding on his views in discussion with Sky Sports, Button added that he didn't feel one single team that had shown itself to be the front runner so far, with another test in Barcelona still to come before the season starts in Australia.

"Different cars are quick at different times and it depends on what tyre you use, and how much fuel you use," he said. "I don't think there is one standout team, or two standout teams, at the moment.

"There might be at the first race but at the moment there's no one that stands out to me in being superior."