Hart was stunned after being axed for City’s opening Premier League win over Sunderland at the Etihad.
He had a face like thunder as he watched on from the bench, before being forced to join his team-mates in the centre circle to thanks fans at the final whistle.
Discussing Hart’s omission Guardiola said: “I’m pretty sure he’s not happy. But he’s not done as much work as Willy Caballero.
“What can he do? We work every day on that, we have boxes and position games and many things, so it was a decision I took for this game.
“All the players who didn’t play, they’re sad, they’re upset, of course. I would not like them to be happy if they would not play.