As Bayern Munich grew increasingly confident that they would be able to sign Sane after pursuing him all summer, the 23-year-old suffered cruciate ligament damage during City's Community Shield win over Liverpool that sees him ruled out for a large chunk of the season.
Pep Guardiola initially suggested a timeframe of six to seven months.
But Low says: "It is extremely annoying that Leroy will miss for a long time, which hurts us because he has become a player after the World Cup, who has had a decisive influence on the team.
"He has the gift of opposing defenders to destabilize with its speed and unpredictability.
"I know from our doctors that the surgery went very well. His knee was stable during the treatment. I reckon he will be back in training in January, so he'll have almost half a year before the tournament starts. I'm of course counting on him."