The Bluebirds were shot down by their London counterparts courtesy of Jay Simpson's first-half double - the club's third loss in four games and their second successive home defeat.
"We didn't really get going at all," said Rae in the Western Mail.
"And I think all the players would agree that nothing happened for us, nothing we tried came off and perhaps it was one of those games.
"But the manager said his biggest disappointment was the lack of effort and maybe he's right. You can't put your finger on why, but that's certainly not something that can be said very often about us.
"But the gaffer was obviously raging and he went through every player and told us what's what. We'll obviously keep what was said in house, but it's obvious we know it just wasn't good enough."