Sirotkin describes Friday practice as "worst run of the year"

Williams driver Sergey Sirotkin has labelled Friday's second practice sessions as his "worst run of the year", and believes it is a "bit weird" to have suffered that on the season-concluding Grand Prix.

Sirotkin finished rock-bottom in 20th in the second practice session, with his best time almost a whole second adrift of his team-mate Lance Stroll.

Robert Kubica was announced to replace Sirotkin for next season on Thursday, and he drove in the Russian's place in FP1.

"(It was) quite a tough session," Sirotkin admitted to Autosport in the immediate aftermath of FP2. "(We) really struggled on the quali runs.

"We will be investigating what it could be, because it's the worst run of the year, that is for sure! So it should be something major, it's not a matter of little things.

"Afterwards, we still had a hope it is probably the (hypersoft) compound, probably something related to that or still to the hot track - but actually on long runs, on primes (supersofts) it felt exactly the same.

"It's been definitely the most difficult FP2 in the season, which is a bit weird to have it here in that moment in such a situation.

"I am really sure we'll find something tonight, because it should be something (as the reason) why we are struggling so much."