Ferrari's Kimi Raikkonen was fastest in the final morning of pre-season testing in Jerez on Wednesday as McLaren and Red Bull's hopes for a problem free day were dashed.

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Jenson Button twice failed to get beyond the pitlane as a nightmare week for the new McLaren-Honda partnership continued.

McLaren racing director Eric Boullier warned on Tuesday that any more setbacks in testing would delay their chances of being competitive once the season gets underway in Australia in six weeks' time.

However, Button managed just seven laps on Wednesday morning to take the team's total for the week to just 51, the same number as world champion Lewis Hamilton completed before lunch despite suffering a spin earlier in the day.

Red Bull haven't faired much better in the southern Spanish city and Daniil Kyvat managed just eight laps before being brought to a halt on track by a power unit problem.

The youngest ever driver in Formula One, Max Verstappen, had no such troubles though as the 17-year-old whizzed around for over 50 laps in his Toro Rosso, setting the third fastest time behind Raikkonen and Hamilton.