Sirotkin was 20th and last in the second practice session, trailing teammate Lance Stroll by nearly nine tenths of a second.
Robert Kubica, whose Thursday confirmation as a Williams driver for next year left Sirotkin without a ride for 2019, had replaced the Russian in the previous FP1 session, and was likewise last.
“Quite a tough session,” Sirotkin said after FP2. “[We] really struggled on the qualy runs.
“We will be investigating what it could be, because it’s been 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.”
Sirotkin reiterated that he found the timing of his poor session “quite strange”.
“I don’t know why it is happening right here in that moment, but it is what it is,” he said.
“Still a day tomorrow which I am looking forward to. It is the last race and I am just trying to enjoy and do the best I can.”
The Russian driver admitted after Kubica’s announcement that he was “very sad” and struggling to believe that he would not be on the grid in 2019.
Asked whether his motivation had taken a hit for Abu Dhabi, Sirotkin said: “I’m not thinking about it at all. When you are in the car, you just think [about] how you drive it.
“And I am just trying to enjoy it, even if I’m honest, it was definitely the least enjoyable session… probably one of those less enjoyable sessions of the year.
“I mean, I still try to find it in this way, try to at least be approaching it in this way. So yeah, no, I didn’t even have this thought for a second in my head when I’ve been in the car.”
Sergey Sirotkin, Williams FW41
Photo by: Glenn Dunbar / LAT Images