The Tottenham player was not even named among the substitutes by Blues boss Alex McLeish and drove away from the ground before kick-off which meant he did not see his team-mates fight out a 1-1 draw.
McLeish said: "I spoke to him and told him he broke a club rule. I understood his disappointment.
"He broke a club rule, he didn't realise the rule, so we won't be taking any action against David."
He added: "We do say to players it would be nice to stay and support your team-mates.
"I realise they don't want to hoover up any good atmosphere or feelgood factor the players may have before a game and they don't want to mope around the dressing room.
"But we do encourage them to see the games and they have to stay around in case there is an injury in the warm-up."
McLeish insisted Bentley will be considered for the two remaining games he is eligible to play in this season, including Saturday's clash at Newcastle.
He said: "Everything is fine. There is no falling out with David. He didn't storm off as people said.
"It is a hyped up expression in the media. He calmly got into his car and went home.
"He is available for the other two games. He can't play against Tottenham but is available for the other two games."
Source: PA
Source: PA