Lewis Hamilton admitted Mercedes are "just a bit lost" with their car after a "very challenging" start to the Singapore GP weekend which has left him concerned about whether they will even make the grid's top 10 in qualifying on Saturday.
With Mercedes aiming to hit back on the streets of Marina Bay following a difficult Baku relative to the front-runners last week, when Hamilton in particular endured a tough weekend after an engine penalty left him starting the race at the back of the field, the team's drivers both struggled with a misbehaving W15 on Friday.
Hamilton finished both sessions outside of the top 10 and while team-mate George Russell fared a little better in the more representative floodlit running to take seventh, his Practice Two ended with a late crash into the barriers.
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In team radio conversations with his race engineer Peter Bonnington during the sessions, Hamilton reported repeat issues with understeer along with traction out of the street circuit's slow, twisty corners.
"The car feels very difficult. A very challenging day," said Hamilton after finishing 11th fastest and 0.982s off the pace set by McLaren's Lando Norris.
"We tried everything set-up wise and nothing seems to work with the set-up. Definitely very challenging.
"We are giving it everything then you find out you are a second off. Ultimately, just a bit lost. Not really sure where to put the car."
Asked about whether set-up changes made to the car between the two practice sessions had made any difference, Hamilton replied: "No. We tried a lot and achieved the same thing."
And on the evidence of Friday's form without improvement, Hamilton predicted: "At the moment we won't be going into Q3."
Russell: We have a lot of work on our hands | Shovlin: Leclerc, Norris ahead of field
Although he may have finished slightly closer to the front, Russell reported similar issues and concerns to Hamilton at the end of the session.
Asked about the crash in the closing moments of P2 which saw him nose the barrier and damage the front of his car at Turn Eight, Russell said: "Not a lot to say, really. Locked up, took the front wing off.
"It was a really challenging Friday for us.
"We were really off the pace; we need to understand why that is. I'm sure we'll find some answers.
"We've made some big changes from FP1 into FP2 but the car's just not really feeling that well connected as it was this time 12 months ago and in recent races, so we need to try and get to the bottom of it."
Although Mercedes did outpace struggling Red Bull, they themselves finished behind both RB cars - the team which proved the day's surprise package - while the gap to the lead McLaren and Ferrari cars was large.
"There are a lot of surprises out there," said Russell, who crashed out late on while chasing victory in last year's Singapore race after qualifying on the front row.
"The VCARB [RB] is really quick, the Williams is really quick. The Red Bulls seem to be off the pace.
"There seems to be a big gap to the McLarens and the Ferraris so as a minimum we hope to be between that midfield gap and the front four. But right now we have got a lot of work on our hands."
Andrew Shovlin, the team's trackside engineering director, described the day as "one of the trickier Fridays of the year so far".
"Neither driver was particularly happy with the balance throughout the [second] session, although we made some progress on our long run," said Shovlin.
"Whilst that second hour of running was more encouraging, we've still got a good chunk of work to do overnight. McLaren and Ferrari, in particular Norris and Leclerc, looked to be a step ahead of the rest of the field. We will have to find some big improvements to be in the fight with them [on Saturday].
"We've also got one eye on some of the teams behind us. We will need to find gains overnight if we are to have a smoother run through qualifying and that is what we are focused on doing."
Sky Sports F1's live Singapore GP schedule
Saturday September 21
8am: F1 Academy Race One
10.15am: Singapore GP Practice Three (session starts 10.30am)
1pm: Singapore GP Qualifying build-up
2pm: SINGAPORE GP QUALIFYING*
4pm: Ted's Qualifying Notebook
Sunday September 22
8.30am: F1 Academy Race Two
11:30am: Grand Prix Sunday: Singapore GP build-up
1pm: The SINGAPORE GRAND PRIX
3pm: Chequered Flag: Singapore GP reaction
4pm: Ted's Notebook
*also live on Sky Sports Main Event
Formula 1's thrilling 2024 season continues live on Sky Sports F1 this weekend with more stunning street circuit action, this time under the lights at the Singapore Grand Prix. Stream every F1 race and more with a NOW Sports Month Membership - No contract, cancel anytime