Walker was shown his second yellow card for a collision with Calvert-Lewin in the first half of the 1-1 draw at Etihad Stadium.
However, Fernandinho thinks that his teammate didn't deserve to be sent off.
"It's tough to say something about a referee's decision, you have to be careful," said the Brazilian. "But we are in the Premier League and it is so demanding. When you have some players who dive and they are so soft, it is a little bit weird.
"But if the referee takes this decision you have to keep going and look for the next game."