Lewis Hamilton has conceded he faces an uphill battle to reach Q3 in Spanish Grand Prix qualifying.
The seven-time F1 World Champion finished only 11th in second practice with Mercedes given its first chance to compile meaningful data from its radical upgrade package that was introduced in Monaco last weekend.
Hamilton's best effort was almost seven-tenths down on session-leader Max Verstappen, but was alarmingly slower than Nico Hulkenberg's Haas, both Alpines and former teammate Valtteri Bottas in the Alfa Romeo.
"It was a difficult day one. Just getting on top of the tyres and the deg, the car feels like a car," said Hamilton.
"It is so different from last week but the long-run pace didn't look terrible, we have just got to work on trying to figure out how we can extract more from a single lap."
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'It won't be easy'
Mercedes drew within a point of Aston Martin in the Constructors' standings with fourth and fifth in Monaco but look set to fall backwards if Friday's pecking order in Spain remains consistent throughout the weekend.
Asked for Mercedes' prospects ahead of qualifying, Hamilton replied: "From the pace I had, it is a struggle for me to get into the top 10. But hopefully, we will do some changes overnight.
"It is very close between us and that middle... after P5 back to P10, it is very close between us all and it is impressive to see the improvements everyone seems to have made.
"If you look at Ocon, the Alpines are doing great. The Aston Martin was second just behind the Red Bull which is really impressive.
"It won't be easy, that's for sure."