Bayern Munich goalkeeper Manuel Neuer, who had been out injured since September before playing for Germany in Saturday's 2-1 defeat by Austria, made the cut.
Asked about Sane's omission, Loew said: "It was a very tight decision between him and Julian Brandt (of Bayer Leverkusen) which went in favour of Brandt". "There are better days in the life of a national team coach, when you have to send four wonderful players, who deserve to be at the World Cup, home". It's like being at the airport check-in counter en route to Moscow and you are not allowed to board the plane'.
Neuer is to join the starting lineup in Russian Federation despite having been out for eight months due to a foot injury, while Sane was passed over after having a stellar season with English Premier League (EPL) champions Manchester City, reported Efe.
That the 32-year-old Neuer has been included means he is expected to remain as captain and first-choice goalkeeper, ahead of Barcelona's Marc-Andre ter Stegen.
Marcus Rashford suffers injury ahead of England's World Cup opener
Gareth Southgate's 23-man squad set off for Russian Federation on Tuesday suited and booted by Marks and Spencer. Southgate added: "I think there was a shift in November when we brought in some of the younger players".
"I always had the goal in front of me".
"I want to thank all those who have accompanied me during my injury; the doctors, the physiotherapists, the physical trainers, the people around me and the people in the national team and at Bayern". German media reported that Loew would have preferred if Sane postponed the surgery and Loew left Sane out of the next two World Cup qualifying games.
Loew announced his squad at the end of a training camp at the Italian Alps.
Germany's preparations continue with a friendly against Saudi Arabia in Leverkusen on Friday.
Germany open their 2018 campaign against Mexico on June 17, before going on to face Sweden and South Korea in their other Group F fixtures.