McLaren fell well short of its aim of putting both its cars in the top-ten in qualifying for the Bahrain Grand Prix, with race director Eric Boullier "astonished" by the team's under-performance.
In an early sign that the session would likely be a complicated one for the Woking-based outfit, Fernando Alonso barely made it into Q2.
Ultimately however, the Spaniard concluded his day in P13, one spot ahead of team mate Stoffel Vandoorne as both MCL33 cars suffered from an inexplicable lack of pace.
"Obviously it’s a bit of a surprise, based on the pace we had in FP3," Boullier told Sky F1.
"There is a need for a big investigation.
"On his last lap Fernando found some pace in Sector 2 and Sector 3, which would have helped earlier. We need to find out what’s going on.
"The balance is fine, obviously there’s a lack of grip, that’s my conclusion for the poor performance, but they don’t report anything wrong."
Alonso vowed to remain optimistic for Sunday's prospects, believing McLaren will once again come into its own in the race, as it did two weeks ago in Melbourne.
"The race pace has been better than quali pace so far for us," said the two-time world champion.
"Definitely we don't start in the ideal position, but it is the way it is. We didn't have more speed today, we need to find some for tomorrow."
Boullier suggested that perhaps the Bahrain layout had been part of the team's week Saturday showing.
"We were struggling last year in Bahrain as well, which is something we need to investigate for this layout," said the Frenchman.
"Our pace in Australia was not a dream, it was real in the race, and we know it will be better here tomorrow than the one-lap pace.
"But we need to find out why. We need to ask some questions at the factory.
"Like all of us on the pit wall, to be honest, I’m a bit astonished and we need to understand what happened."