The 33-year-old left Arsenal in acrimonious circumstances after refusing to join the club’s pre-season tour of the United States.
Arsenal were made to kowtow to Koscielny’s demands after sanctioning a £4.3m sale to French club Bordeaux before acquiring the services of David Luiz from Chelsea as his replacement.
Koscielny, who joined Arsenal from Lorient in the summer of 2010 and made 353 appearances for the club, was widely criticised for the way he left but he maintains the physical demands of the Premier League was something he could no longer cope with.
Koscielny told L'Equipe: 'A Premier League season is very long. It requires a lot physically and mentally.
'I didn't feel I could play 40-50 matches and I didn't want to end my career with injuries. I've gone down a level, but to take more pleasure.
'Either I finished there or changed clubs. With my family, we felt it was time.
'Everything was in my thinking: football, my physical state, my wife, my children, the daily life we could have.
'I can only say that I left with my head held high.
'All of those I worked with for nine years... everyone respected my decision to return home with my family.'
Koscielny has made eight Ligue 1 appearances for Bordeaux so far as his new club sit fourth on the table.
