Sane, who won the PFA Young Player of the Year following a splendid Premier League winning season with City, had been expected to go to the World Cup.
But when Germany announced the final squad tasked with defending the World Cup, the 22-year-old's name was mysteriously missing from the list.
Goalkeeper Bernd Leno, defender Jonathan Tah, both of Bayer Leverkusen, and Freiburg late bloomer Nils Petersen have also been left out of the 23-man group.
Goalkeepers: Manuel Neuer (Bayern Munich), Kevin Trapp (PSG), Marc-Andre ter Stegen (Barcelona)
Defenders: Mavin Plattenhardt (Hertha Berlin), Jonas Hector (Koln), Matthias Ginter (Borussia Monchenglach), Mats Hummels (Bayern Munich), Niklas Sule (Bayern Munich), Antonio Rudiger (Chelsea), Jerome Boateng (Bayern Munich), Joshua Kimmich (Bayern Munich)
Midfielders: Sami Khedira (Juventus), Julian Draxler (PSG), Toni Kroos (Real Madrid), Mesut Ozil (Arsenal), Leon Goretzka (Schalke), Sebastian Rudy (Bayern Munich), Julian Brandt (Bayer Leverkusen), Ilkay Gundogan (Manchester City)
Forwards: Timo Werner (RB Leipzig), Marco Reus (Borussia Dortmund), Thomas Muller (Bayern Munich), Mario Gomez (Stuttgart)
Germany are the early favourites to win this year's World Cup. Should they be victorious, Joachim Low's team would become the first since Brazil in 1962 to successfully retain the World Cup, and only the third in history after Italy also managed it in 1938.