The Daily Mail says Sane's mother Regina Weber, West Germany's 1984 Olympic gymnastics bronze medalist, has proved obstructive as City attempt to tie down one of their prized assets.
City have been discussing fresh terms with Sane since last summer with his current deal running until 2021.
The Premier League champions, who declined to comment on the subject on Wednesday, have always maintained they expect the 23-year-old to sign an extension. Sane has also publicly stated that the Etihad Stadium feels like 'home'.
Sane's father, the ex-Senegal international striker Souleymane Sane, officially represents him with the help of intermediaries based in England but his mother has become involved in talks.