Argentine defender Zabaleta was sent off at the Nou Camp for two bookable offences, picking up his second booking for his protests to Lannoy over his failure to award City a penalty when Edin Dzeko appeared to be felled by Gerard Pique inside the box.
Barcelona also had a strong penalty appeal of their own waved away in the first half, while the home side had a goal controversially ruled out for offside even though replays showed Jordi Alba was onside before he crossed for Neymar to score.
Zabaleta was insistent that City should have had a penalty for the Dzeko incident and he claims he is in the dark as to why he was sent-off.
Pablo Zabaleta: "It was very clear.
"I think Pique was behind me and made the tackle on Dzeko and the referee was only two metres away from that.
"I don't know why I was sent off. I went to him to talk to him in a good way.
"I was a little bit angry to him because he didn't give a penalty but I have always been very respectful to him.
"I am frustrated. I think it was a shocking decision.
"Sometimes in the game you are nervous because you are trying to get the result, and sometimes shocking decisions by the ref make you a bit angry.
"It was also a foul against Dzeko just before Barcelona's first goal.
"He held the ball and turned, and Pique had hold of his shirt, and the ref gave a free-kick to Barcelona.
"I am disappointed but also very proud of the team because I think we played a fantastic game.
"We tried from the beginning until the end, should have scored first and had more chances in the game."