PORTO, Portugal -- Cesc Fabregas believes Diego Costa has been treated "unfairly" by English football authorities, and says the striker is "rightly" frustrated with the situation.
Costa was given a three-game ban by the FA for violent conduct, after an incident with Laurent Koscielny in Chelsea's 2-0 win over Arsenal on Sept. 19.
Despite replays showing that the striker was involved in a number of off-the-ball incidents missed by the officials, Fabregas felt this was unjust.
"He's frustrated, obviously, and rightly so," Fabregas said. "We all know the causes [of] why he is. Some people understand it, some people don't. It's very unfair what happened to him.
"Apart from that, he's a key player for us, our striker, a player who has to score our goals and finish our combinations. We expect a lot from him.
"If you want to win this competition we all have to be at the top of our game, but you need your big players to perform. He's one of them, for sure."
Chelsea manager Jose Mourinho agreed with Fabregas' view, saying there was a "desire" to suspend Costa. The Portuguese had been asked how his team would be doing with 11 Costas in the team.
"I think we would lose every game because the desire to suspend him is so big we wouldn't have players to start the game. So I'm happy we have only one and let him play until they decide to suspend him again."
Fabregas also insisted that Chelsea are not suffering from "complacency" despite a dismal start to the season that has seen their title defence begin with just eight points from seven games. The champions are 15th in the table after a series of flat performances.
Fabregas stressed the team would improve and that manager Jose Mourinho would not allow complacency seep in.
"It's not complacency," Fabregas said. "It happened to Manchester City a bit last season. Maybe it is mental, something inside you, but this team works well. The manager would never allow us to be complacent.
"We are training well, motivated. Maybe things are't going the way we want at the moment, but I'm sure we can turn it around. Tomorrow -- Champions League, Porto away -- is a great moment to do that.
"If we want to start playing as well as we did last season, we have to start performing in big games like tomorrow."
Fabregas also maintained that Chelsea could still win the league.
"Well, whatever happens inside the dressing room is not for talking about in here," he said. "Obviously, we have to improve. It's not about the coach telling us things or for him to be upset that we have to perform. We have to perform because we are winners, we play for Chelesa, and we want to perform every game. Not because the manager comes to us and is upset. It has to come from us.
"We are not babies. We are not players who started playing right now. It's true we have a young squad, but that's no excuse.
"We won the league last year. There's no reason why we shouldn't do it again this year. We have to start performing again from now."