Honda boss Yusuke Hasegawa has promised to improve the engine in Fernando Alonso's McLaren
McLaren are in their third season of being supplied with Honda power units and have yet to finish better than fifth in a single Grand Prix since abandoning Mercedes after 20 years of partnership.
And Express Sport understands they are exploring a return to Mercedes with a break clause said to be available at the end of the current season.
But Yusuke Hasegawa was quick to point out that the issues from pre-season testing in Barcelona had been fixed.
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"The problem that we had in the testing, every single reason [for the problems] we tried to modify the engine, but from the performance point of view we are still struggling to extract more power from the engine," the Honda boss said.
"Actually it is different from the test situation.
"But I hope reliability issue was fixed already."
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McLaren-Honda have been struggling with reliability since pre-season testing
Yusuke Hasegawa is under pressure from McLaren to produce more power
Honda are said to be working night and day to make up the gap on their rivals but Stoffel Vandoorne was still forced to do a manual restart of the engine during the race after losing power.
McLaren driver Fernando Alonso's race was in fact ended by a suspension failure but the Spaniard has previously claimed the car is as much as 20mph slower on the straights.
And while Hasegawa appears confident the speed will come, the time-frame is not clear.
"I cannot guarantee when we can get the power, but as soon as possible of course we will try to introduce a new specification for that," he added.
"But it is not a one-day job.
"In a month's time or two weeks' time I would like to try, but I cannot guarantee here.
"As soon as I can prepare that I am happy to introduce that."