Jenson Button admits that the second day of the final F1 test of the winter in Bahrain has proven that rivals Red Bull Racing will be on the pace during the 2014 season - if it can keep its new RB10 on track.

While a gearbox issue hampered his own programme as McLaren ended the day fifth on the timesheets, Daniel Riccardo was third quickest for Red Bull as the defending champions enjoyed its best day of the winter so far.

Speaking with members of the media afterwards, Button said he had no doubt as to the pace of the new Red Bull and said he was sure they would be in the mix come the season opener in Australia if the technical issues faced so far can be resolved.

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"When that car [the Red Bull] goes round, it will be quick," he said. "Daniel was running the soft tyre and I was on the medium which makes a difference, but they are quick and if they can do a race distance, they will be towards the front. I think we are quicker than them in a straight line but they are quicker in other areas and we have to aim to improve in that respect. I was running on track with him for a few laps and and he couldn't pass me on the straight but then he got ahead at turn eleven which was an interesting experience that I hadn't seen before..."

Button added that part of the focus for McLaren in the remaining two days of running would now be on set-up as it works towards the opening race of the campaign, with the team still seeking to fully unlock the potential of its 2014 challenger.

"We have a lot of work to do still, but the basic car is good," he said. "We are waiting for upgrades, but there is a good feel and we have a good understanding of the power unit. Outright pace is something to work on as our focus has been on mileage at the moment and we'll know more on where we stand in the next few days when we've worked on set-up a bit more.

"It's hard to tell at the moment as you don't know what people have added in terms of upgrades but Mercedes are quick, Williams are strong and Force India look competitive - as do Red Bull and Ferrari. It's changing all the time and there is a lot of guesswork going on. People say they are focused on themselves but that's complete cr*p as you always look at the times and see what others are doing - it would be stupid not to.

"We know we have work to do as a lot of cars are going to be competitive and it will be a lot tighter on the grid in Australia than a lot of people thought it would be this time last week."