Jenson Button's bid to conform to Formula One's new controversial weight limit has been hampered by an infection to his knee.
After twiddling his thumbs on the opening day of pre-season testing on Tuesday due to technical issues with the new McLaren, the 34-year -old was top of the timesheet on day two.
The times, however, are largely irrelevant at present given the steep curve the teams are on when it comes to learning about the new cars in light of a raft of regulation revisions.
One of those has seen the weight limit of car and driver combined rise from 642kg last year to 692kg this season.
But that is arguably not enough for the taller drivers such as Button given the arrival of the new powertrains, in conjunction with the new energy recovery system that have made the cars significantly heavier.
Previously on the limit anyway, Button has been forced to diet further, but has revealed he needs to lose more weight ahead of the season-opening race in Australia in mid-March due to a knee problem.
"I did a hell of a lot of training over the winter in terms of diet, really limiting my intake, but in a safe way," said Button.
"But that's all gone out of the window in January. I haven't trained for three weeks because I've had an infection in my knee.
"And when you are sat on your backside all day like on Tuesday, you want to eat, so it's not been the easiest.
"Right now I'm not as light as I will be at the first race, but I'm definitely going to lose another kilo by race one, and it's going to be tight."
At least Button was happy with the baseline of his new car as opposed to a year ago, when McLaren built one that failed to claim a podium for the first time since 1980.
On this occasion, a relieved Button said: "I enjoy driving this car.
"Our first day last year we were quick, but the car had its flaws and we could see that. This time we don't have those issues.
"The basic car itself is good and it works. No scary things with it. I'm really looking forward to getting back in it."
In sharp contrast, reigning champions Red Bull and Vettel, along with engine partners Renault, suffered a second successive day of woe.
Vettel departed the circuit early on Wednesday after completing a total of just 11 laps over the two days due to issues with Renault's new systems.
A frustrated Vettel said: "With such big rule changes it's usual to have teething problems, and that's what tests are for, to sort those issues out."
F1 2014 car launch - The era of the 'anteaters'
F1 2014 car launch - The era of the 'anteaters'
1/17 McLaren - MP4-29
The Woking-based outfit launched their MP4-29 on January 24, with drivers Jenson Button and rookie Kevin Magnussen joined by reserve driver Stoffel Vandoorne. However, the main talking point was the absence of team principal Martin Whitmarsh following the return of Ron Dennis
2/17 Williams - FW35
Williams were the first to unveil their car, albeit a computer-generated design. The real thing is yet to roll out of the garage at Jerez, with some last minute adjustments holding up its debut. Former Ferrari driver Felipe Massa joins the team to try and return them to the top of the sport, and he will partner Valteri Bottas who is retained from last season
3/17 Ferrari - F14T
The Italian manufacturers have pushed Red Bull hard in the past few years, but they hope the F14T will finally surpass their rivals and give either Fernando Alonso or the returning Kimi Raikkonen another World Championship to add to their collection
4/17 Ferrari - F14T
Raikkonen gets reacquainted with the Ferrari cockpit after a four-year absence from the prancing horse, but...
5/17 Ferrari - F14T
His joy is short lived as he becomes the first to suffer from unreliability as his car stops on track, requiring a lift back to the pit lane. He certainly won't be the last though
6/17 Sauber - C33-Ferrari
Sauber have followed the 'anteater' nose design for 2014, and hope for a more successful year than last with Adrian Sutil joining Esteban Gutierrez at the wheel
7/17 Lotus E22
Lotus launched their 2014 challenger, the E22, on the same day as team principal Eric Boullier left the team, with Gerard Lopez replacing him at the helm. With Romain Grosjean now the team leader, many will be watching how he and livewire Pastor Maldonado get on this year. Thta's if they turn up, as their absence from Jerez doesn't bode well
8/17 Mercedes - W05sup
Nico Rosberg and Lewis Hamilton unveil the Mercedes W05sup at Jerez, which thankfully avoids the 'anteater' nose
9/17 Mercedes - W05sup
Many are tipping Hamilton and Rosberg to take the fight to Red Bull this year with the W05sup undoubtedly one of the nicer looking cars on this season's grid, but will it be as fast?
10/17 Red Bull - RB10
Sebastian Vettel and Red Bull are going for a record-equalling fifth straight drivers' and constructors' championship. They have also avoided the 'anteater' nose, and rival Mercedes for the best looking car of the year award. Is there anything Red Bull don't want to win? Daniel Ricciardo makes the step-up from Toro Rosso to replace the now absent Mark Webber
11/17 Toro Rosso - STR9
Toro Rosso's design sure isn't pretty, but they have taken a step into the unknown with rookie 19-year-old Daniil Kvyat. The Russian impressed in practice towards the end of last season, but how will he get on against his more experienced team-mate Jean-Eric Vergne?
12/17 Toro Rosso - STR9
The 'anteater' nose of the Toro Rosso SRT9, likened to a sex toy by lingerie makers Ann Summers
13/17 Force India - VJM07
The ever-impressive Nico Hulkenburg returns to the team he left at the end of 2012 having missed out on a seat at Ferrari, Lotus and McLaren. The German will have a point to prove once more, but he'll have a difficult enough time to beat team-mate Sergio Perez first
14/17 Caterham - CT04
After a short delay which saw their early morning unveiling cancelled, Caterham eventually rolled out their CT04 in the afternoon, with another rookie in Marcus Ericsson at the wheel, while the returning Kamui Kobayashi took the picture
15/17 Williams - FW36
Williams finally got their FW36 running after a delay on day one of testing at Jerez, with Valteri Bottas taking to the track
16/17 Marussia - MR03
Two days later than scheduled, Max Chilton eventually left the garage in the Marussia MR03 for its first run at Jerez
17/17 Marussia - MR03
Chilton brings the car back in after completing an installation lap