"City's failure has been a massive story," said Santa Cruz to the Mail on Sunday.
"Everyone hoped to see City as contenders to win the Champions League because of the investment they made.
"They aren't one of the clubs with tradition in the Champions League so they probably didn't realise the expectations. But people were really disappointed with their performances not to get past the first round with the players they have. That's the way they felt it here.
"It is hard to know why. I think the key is to get a good start. There are no weak teams in the Champions League, every team can cause problems if you don't perform in the proper way, and City found that out."