Fifa has written to all 32 teams competing at the World Cup telling them to "now focus on the football" following a controversial build-up.
Host Qatar has been criticised for its stance on same-sex relationships, its human rights record and its treatment of migrant workers.
The tournament starts on 20 November.
The letter urges that football should not be "dragged" into ideological or political "battles" and it should not be "handing out moral lessons".
Peaceful protests have been planned by some players.