McLaren’s troubled pre-season suffered yet another setback with the team forced to abandon running on the first day of the final Barcelona test after just seven laps.
The team have been rooted to the bottom of the mileage charts ever since the new Honda-powered MP4-30 made its debut at the Jerez test at the start of February with a succession of problems limiting the car's mileage
On the back of a first Barcelona test at which McLaren suffered repeat issues with a seal on their ERS unit and then saw Fernando Alonso crash out, Jenson Button was on track at the Circuit de Catalunya for just one timed lap on Thursday morning before the team were forced to call a halt to proceedings.
"After just seven laps, Jenson noted a vibration and brought the car back to the pits, where we discovered a hydraulic leak that required a full power-unit change," McLaren said in a statement.
"The time required to complete the change unfortunately meant that our running for the day was over before lunchtime."
Whereas world champions Mercedes have passed 1000 laps for the winter, McLaren have been on circuit for barely more than 200 and are firmly on the back foot with just two weeks to go until the season-opening Australian GP.
Amid the team's reoccurring problems at last week's Barcelona sessions, Button conceded that the revived McLaren-Honda partnership may not be completely ready for the Melbourne event - although stressed that the MP4-30, despite its lack of laps, didn't have any fundamental flaws and the team would improve as the season progressed.
Speaking earlier on Thursday, McLaren chairman Ron Dennis told reporters that "we are at the foot of a very steep mountain" with the MP4-30.
With Fernando Alonso ruled out of the final test while he continues his recovery from his testing crash last Sunday, Button will return to the MP4-30 as McLaren attempt to recover lost ground on Day Two.