Sirotkin took part in his first and only F1 season to date in 2018 with Williams but was replaced the following year by Robert Kubica, who made a return to F1 after a seven-year absence
"I'd say it's become maybe even more painful," Sirotkin told Autosport. "Because at that point, of course, Williams wasn't the most competitive, I knew that for the next year the situation probably wouldn't change dramatically.
"[We thought] that having this gap year we'd maybe have the chance to find a better option than trying to fight Robert for that seat.
"But now, having harboured some rather high hopes, high expectations, and even having had some initial agreements [in my first year in F1], and in the end, you didn't achieve your target.
"Having then lost a further year, you realise that to make it [back to the grid] for the following year will be even tougher."
Sirotkin explained how he initially felt as if he would find it difficult to adjust to attending races and not participating after 2018 but noticed after delays with his passport and subsequently missing a race because of it, he prefers to attend race weeks anyway.
"In the paddock, everything is familiar, you're involved, but you don't have a car, you're not doing much, you're still watching the races on TV or on the computer, and at some point, I thought this may be harder to accept," Sirotkin commented.
"But then I missed one race due to a passport delay, and after that I realised that I do prefer to fly in, to remain in that system in one way or another, to remain in touch with the people I know, rather than watch it from home on the couch."
Bahrain International Circuit - Winter testing