New Honda motorsport boss Yusuke Hasegawa says there are still elements of the new power unit that need more testing for reliability, as technical issues brought about an early end to the third day of testing for McLaren.

Following its dismal 2015 season, Honda has been pushing hard to recover the sizeable power deficit to its rivals, but while it has made improvements relative to last year, it is still anticipated to be lagging compared with at least Mercedes and Ferrari.

Indeed, Hasegawa - who is replacing outgoing Honda motorsport boss Yasuhisa Arai - says the focus remains on bolstering the power unit's reliability first and foremost, but while he is happy with the progress, he says there are still some unknowns.

"In general we checked our reliability on the dyno, so we have already confirmed our engine is running on the dyno for over 4,000km, but of course we have to check in the car itself," he said.

"Reliability is one of the most important things as an update from last year to this year. Still we have some minor troubles for the parts, so that we have to confirm that every part can go right through the race.

"From an operational point of view, definitely yes. Yesterday we ran over 100 laps but to achieve over 4,000km this is not long enough!"

It comes as McLaren was forced to end its third day of testing early after the MP4-31 - being driven by Jenson Button - developed a hydraulic leak. The Briton had completed 51 laps.