Mercedes boss Toto Wolff says Valtteri Bottas performance level has improved lately although he reckons the Finn still needs "the tick of a killer".
After a performance slump which depreciated his results over the summer compared to world champion team mate Lewis Hamilton, Bottas has slowly improved.
He secured pole for the Brazilian Grand Prix, a result largely facilitated however by Hamilton's crash in Q1, and appeared to be in with a strong chance of clinching his third win of the season on Sunday, but was ultimately outrun from start to finish by Sebastian Vettel's Ferrari.
Wolff was satisfied with his driver's efforts however, underlining the difficult task he faced.
"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.
"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."
Taking into account Hamilton's remarkable run to fourth after starting from the pitlane, and with his team mate just a handful of seconds up the road in the end, the disparity in performance between the two Mercedes drivers was clear for all to see.
Yet Wolff wasn't surprised, believing Bottas is on the right path, although he still has his work cut out to give Hamilton a proper run for his money.
"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.
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