The Parkhead side are reportedly close to sealing a €5m move for the Swedish international centre-back as a replacement for the soon-to-be departing Kristoffer Ajer with a medical believed to have already taken place as talks progress.
Speaking to Russian media outlet Match TV about the potential loss of Starfelt, the Rubin boss said: "These are the rules of the game. If we receive an interesting offer that is beneficial to everyone, we are forced to accept it.
"This confuses plans a little, but such a situation can always be laid. It is possible that someone else will leave us this summer.
"This is normal. I'm glad this is happening. When the transfer takes place officially, it will be the largest transfer."
The 26-year-old, who joined Rubin Kazan sin July 2019, made 31 appearances in all competitions last season, scoring three goals.