Toure was also dropped at the start of last season, sparking a row between the club and his outspoken agent Dimitri Seluk which led to a longer period of isolation for the Ivorian.
That was eventually resolved, with Toure not only winning back his place but doing enough to earn a new contract.
However, Toure has again been left out of the squad by Guardiola and the manager raised fresh doubts over the veteran midfielder's future by refusing to make public why.
"I spoke with him and he knows the reason why, but it's between him and me," said Guardiola. "It's a 'sportive' decision. Hopefully he'll play soon, but it depends on him."
Elsehwere, Vincent Kompany did not make the trip having failed to sufficiently overcome the calf injury which ruled him out of the Liverpool game.