Mercedes Formula 1 boss Toto Wolff says Valtteri Bottas is still missing "the tick of a killer", although he reckons the Finn has started to recover from his slump.
Bottas secured pole position for the Brazilian Grand Prix, but he was beaten to the race victory and ended up just 2.7 seconds ahead of his pitlane-starting teammate Lewis Hamilton.
With little to separate Mercedes and Ferrari in pace terms, Bottas effectively lost his best chance of the win when he got too much wheelspin away from the line and lost the lead at the first corner to eventual race winner Sebastian Vettel.
But the way in which Hamilton brilliantly battled through the field, and came home just 5.4 seconds adrift of Vettel, has prompted suggestions that Bottas should have been able to do more to put the pressure on Vettel.
Wolff admits that there was a clear pace disparity between Hamilton and Bottas in the race, but was not too alarmed by what he had seen.
Bottas, who has struggled to match Hamilton after the summer break, has made progress, according to Wolff, but he reckons the Finnish driver is still lacking his teammate's killer instinct.
"I think Lewis the whole year has been rock and roll, and Valtteri has recovered slowly but still needs the tick of a killer," said Wolff.
"But you must not underestimate that in traffic against the Ferraris it was pretty difficult.
"You can see that at the end, when Ferrari switched the engine on, there was not much difference between the cars. Therefore you cannot expect easy overtakes."
With little hope of Bottas being able to overtake Vettel on track, Wolff admitted that Mercedes gambled with an early pitstop to try to undercut Ferrari.
"Valtteri had a solid race. He lost it at the start," said Wolff. "The initial getaway was good but there was too much wheelspin through the gears and if the gap is so close between the cars then there is not a lot in it.
"Our undercut was a little move of desperation because we couldn't get too close, and we knew that probably it lacked half a second – but nevertheless we gave it a go and the result was as expected."