Mark Webber has hit out at Williams's 2018 driver lineup.
Sirotkin pairs with Lance Stroll, making it among the youngest, least experienced but also the most lucrative 'pay driver' Formula 1 lineups of all time.
Former Williams driver Webber told Metro when asked how he feels about the pairing: "Not happy.
"There's not a person out there that doesn't want to see Williams do well, and to do that they need a marriage between experience and the future.
"You need chemistry between the drivers. F1 isn't a finishing school, it needs drivers who can deliver from the off."
The 2018 season begins in Melbourne this weekend.